Stitching Yarn Research Articles

Simulation of the tensile behaviour of biaxial knitted fabrics produced based on rib structure using a macro constitutive model

This study presents a macro-scale constitutive model to simulate the tensile behaviour of biaxial weft knitted fabrics produced based on a 1 × 1 rib structure. Fabrics were produced using polyester yarns as stitch yarns and nylon yarns as straight yarns in a modern flat knitting machine. Stress–strain curves of 1 × 1 rib structure and corresponding biaxial knitted fabric were measured in three different directions (course, wale and 45 degrees) on a tensile tester. Based on extracted results, a constitutive equation was proposed for macro modelling of biaxial knitted fabrics. The stiffness matrix of the biaxial knitted fabrics was assumed to be a combination of the stiffness matrix of 1 × 1 rib and reinforcement yarns. A UMAT subroutine was provided to implement the constitutive behaviour in Abaqus software. To evaluate the accuracy of the proposed model, fabric tensile behaviour in 22.5° and 67.5° directions were simulated and compared with experimental results. The results showed that the macro model can successfully predict the tensile behaviour of the biaxial weft knitted fabric in different directions.

Design and properties of shape memory sports bras for comfortable pressure based on ergonomics

To improve the difficulty in wearing and uncomfortable pressure of the sports bra, shape memory polyurethane filaments (SMPUFs) were used to prepare seamless sports bras in this study. Five fabric samples with different stitch structures and yarn were prepared. Then shape memory sports bras were designed based on the properties of the different fabric samples and female body characteristics. SMPUFs were characterized by differential scanning calorimetry for the thermal properties. Shape memory properties and mechanical properties of the SMPUFs, covered yarn and fabric samples were measured. Besides this, the moisture absorbency, permeability and thermal resistance of fabrics were tested. A pressure test system was set up and the pressure of the sports bras was investigated at different temperatures. The results showed that the transition temperature ( Ttrans) of the SMPUF was 27.33°C, which could be triggered by human skin temperature. The best shape fixity ratio of the fabric sample was 82.5% and the shape recovery ratio was 94.4%. The comfortable pressure of the shape memory sports bra at the mean human skin temperature of 34°C was 1.6–5.6 kPa.

Structural design and mechanical properties of glass fiber weft-knitted biaxial tubular fabrics

In order to design glass fiber weft-knitted biaxial tubular (WKBT) fabric with the excellent dimensional stability and outstanding mechanical properties, six kinds of WKBT fabrics were prepared by four kinds of knitting structures (1 + 1 rib structure, face plating structure, back plating structure and face and back plating structure) and two kinds of stitch yarns (polyester and polytetrafluoroethylene fiber). The tensile properties, tearing properties and bursting tearing properties of WKBT fabrics with different binding tightness were investigated. The results showed that the failure of WKBT fabric was composed of the breakage of insertion yarns and the breakage of knitting structures. The tightness of knitting structures have significant effect on the mechanical properties of WKBT fabric. Compared with 1 + 1 rib structure, the plating structure affects the mechanical properties of WKBT fabrics by improving the weft density, binding tightness and dimensional stability. The kind of stitch yarn is another factor that affects the mechanical properties of WKBT fabrics.

Influence of carbon fiber non-crimp fabrics stitching parameters on the out-of-plane permeability in liquid composite molding process

The widespread use of carbon-fiber-reinforced plastics (CFRP) has attracted many industries such as defense, and aerospace as well as in sailboats, automotive, and rotor-blades, where high strength-to-weight ratios are required. For the aerospace and defense customer today, the importance is no longer just on minimum weight and therefore performance, but primarily on cost of ownership. Textile-manufactured composites, particularly of non-crimp fabric (NCF) type offer significant cost savings in terms of reduced labor time and higher deposition rates over the unidirectional prepreg tape which is the most traditional method. Vacuum vacuum-assisted infusion method is the most used production technic in CFRP parts which also offers high fiber ratios. The most important goal is the impregnation of carbon fiber package in a through-the-thickness direction to get good quality parts in infusion. The behavior of the impregnability depends mainly on the out-of-plane permeability of the fabric. The fiber type, orientation of the fibers, and the stitching parameters, mainly influence the permeability of the fabric. In this study, the influence of textile parameters on the out-of-plane permeability of UD (unidirectional) carbon fiber NCF was investigated. The stitching yarn parameters (stitch pattern, stitch tension, and stitch length) were varied to see the influence on the out-of-plane permeability. The out-of-plane permeability was measured using a tailored visual flow front monitoring method by measuring resin flow distance on the X and Y axes of the fabric during infusion. The results show that the out-of-plane permeability of the UD (0°) carbon fiber NCF is significantly affected by the stitch pattern, stitch tension, and stitch length.

An analytical friction model for fibre tow slippage in Tailored Fibre Placement preforms based on pull-out experiments

Fibre tow slippage in conventional reinforcement forming is a major defect which can be turned into an additional degree of freedom in preforms made by Tailored Fibre Placement (TFP). Controlling slippage of reinforcing fibre tows, which are deposited on a conventional reinforcement using the TFP technology, is an advantage which enlarges the preform design space Fial et al. (2018). Moreover, when TFP is used to locally reinforce a conventional reinforcement, slippage of the deposited fibre tow during forming, is required depending on its orientation relative to the conventional reinforcement layout to avoid defects. Therefore, characterizing the friction behaviour of the reinforcing fibre tows is necessary to take advantage of its slippage as an additional degree of freedom. In this paper, an analytical friction model describing the interactions of the fibre tows with the backing material and the stitching yarn in TFP preforms is developed based on pull-out experiments. A parametric study allows expressing the parameters of the analytical friction model as function of the stitching parameters.

An experimental and numerical investigation of energy absorption of sportswear in seam area

This study aims to investigate the energy absorption of seam areas in sportswear. Weft knitted fabrics with two structures of plain and rib were fabricated by polyester/Lycra and viscose/ Lycra yarns. Fabrics were stitched in two stitch classes. Moreover, two types of seams were considered. A pull-out test was carried out on all samples to determine the energy absorption values. Furthermore, a finite element model was applied to predict the energy absorption of each structure. The unit cell of each sample was created in ABAQUS software and the tensile load was applied to the stitch yarn. The unit cells of the fabric and the stitched section were modeled in the meso-scale and then elastic and viscoelastic properties of the yarns were assigned to the model. The energy absorption of the sample with rib pattern, lapped seam, and 607 stitch class was more than other samples. Also, the numerical and experimental results showed a high correlation with each other in samples with 304 stitch class and flat seam type.

Factors Influencing Bursting Strength of Single Jersey Knitted Fabrics

The purpose of this article is to assist engineers in making quick decisions to improve the strength of single jersey knit fabric. This article focused on the different parameters of the single jersey knit fabrics (like stitch length, yarn count, GSM, tightness factor, and fabric thickness) are considered to know their influence on the bursting strength. Five hypotheses have been developed for plain, pique, and fleece knits. Analyses of Variance (ANOVA), correlation coefficient, and regression analysis are executed using the STATA 14.1 program to test the hypotheses at a 5% level of significance. Three of the five hypotheses are rejected. This study supports that the bursting strength of the fabric is dependent on the tightness factor, stitch length, and count of the single jersey knitted fabrics. Here, the stitch length, count, and tightness factor are inversely proportional to the bursting strength. The GSM and fabric thickness have less impact on the bursting strength.

A systematic investigation for mode-I fracture properties of stitched composites

Three-dimensional stitched composite (3DSC) is one kind of 3D textile structural composite with higher performance on the interlaminated properties. This work demonstrates a systematic analysis of the Mode I fracture behavior of the 3DSC by designing the stitch pitch and fineness of the stitch yarn in the experiments. In the finite element model, a mixed model combining the homogeneous and microstructural parts was developed to reveal the mechanism of stitch pitch and fineness of the stitch yarn on the mode I fracture behavior of the 3DSC. The results show that the effect of the stitch pitch on the mode I fracture behavior of the 3DSC is related to the crack propagation length of the first stitch yarn, which is also dependent on the tension properties of the stitch yarn. The thickness of stitch yarn can significantly improve the fracture toughness of the 3DSC. However, the relative improvement efficiency of the stitch yarn gradually decreases with the rise of the yarn fineness. According to this phenomenon, this work proposed an optimized design to improve the mode I fracture properties of the 3DSC.

Structural modelling of 100% cotton single jersey fabrics for optimum UV protection

PurposeLightweight, open construction cotton knitted fabrics generally do not impart good protection from solar ultraviolet radiation (UVR). As lightweight 100% cotton single jersey is highly cherished for summerwear, it is sine qua non to understand the structural parameters that effectively strike a good balance between UV protection and thermophysiological comfort of the wearer. Relatively heavy fabrics protect from UVR, but comfort is compromised because of waning porosity, increase in thickness and thermal insulation. The purpose of this paper is to engineer knits that will bestow maximum UV protection while preserving the thermophysiological comfort of the wearer.Design/methodology/approachIn total, 27 cotton single jersey fabrics with different areal densities and yarn counts were selected. Ultraviolet protection factor (UPF) was calculated based on the work of Imrith (2022). To précis, the authors constructed a UV box to measure the UPF of fabrics, denoted as UPFB. UPFB data were correlated with AATCC 183-2004 and yielded high correlation, R2 0.977. It was concluded that UPF 50 corresponds to UPFB 94.3. Thermal comfort properties were measured on the Alambeta and water-vapour resistance on the Permetest. Linear programming (LP) was used to optimize UPFB and comfort. Linear optimization focused on maximizing UPFB while keeping the thermophysiological comfort and areal density as constraints.FindingsThe resulting linear geometrical and sensitivity analyses generated multiple technically feasible solutions of fabrics thickness and porosity that gave valid UPFB, thermal absorptivity and water-vapour and thermal resistance. Subsequently, an interactive optimization software was developed to predict the stitch length, tightness factor and yarn count for optimum UPFB from a given areal density. The predicted values were then used to knit seven 100% cotton single jersey fabrics and were tested for UV protection. All seven fabrics gave UPFB above the threshold, that is, higher than 94.3. The mathematical model demonstrated good correlations with the optimized parameters and experimental values.Originality/valueThe optimization software predicted the optimum UPFB reasonably well, starting from the fabric structural and constructional parameters. In addition, the models were developed as interactive user interfaces, which can be used by knitted fabric developers to engineer cotton knits for maximizing UV protection without compromising thermophysiological comfort. It has been demonstrated that LP is an efficient tool for the optimization and prediction of targeted knitted fabrics parameters.

Effects of stitching yarn types on flexural fatigue properties of 3D stitched carbon fiber composites

This work investigated the static bending and flexural fatigue properties of 3D stitched composites with different stitching yarns. The carbon and PBO fibers were adopted to reveal the effects of stitching yarn types on the fatigue characteristics and failure propagation of 3D stitched composites at low-stress levels by a high-speed camera. The results show that different stitching yarn types affected the static flexural strength of 3D stitched composites but did not affect their modulus. In addition, different stitching yarn types changed the fatigue failure mechanism of 3D stitched composites. The fatigue life of 3D stitched composites can be effectively improved by using PBO fibers since the PBO fiber can effectively delay shear crack growth and prolong the period of the catastrophic failure stage. This work proposed a new scheme for improving the mechanical properties of stitched composites.

Topology based modelling of crochet structures

Crocheted textiles receive scarce scientific study and are at present not produced in automatized industrial scale. Computer-aided modelling and simulation offer capabilities for investigating possible technical fields of application. In this context a novel approach for modelling crocheted textiles consisting of chains, slip stitches and single crochets using a topology based and parameterized key point representation at the meso scale is proposed. According to the stitch size, yarn diameter and pattern spline interpolated models, which are free of interpenetrations up to approximately a 1/10 ratio of yarn diameter to stitch size, are generated by a developed Python program and software from the company TexMind. The models are suitable for finite element method (FEM) applications with LS-DYNA with which the mechanical properties of crocheted textiles can be studied. Exemplary simulations show anisotropic properties and homogeneous distribution of stresses in a crocheted textile. Due to the computationally simple and flexible modelling the presented approach may serve as a tool for designing planar crocheted textiles. This allows for estimation of the required yarn length and offers the prediction capabilities of simple and fast FEM simulations based on beam elements.

Effects of stitch yarns on interlaminar shear behavior of three-dimensional stitched carbon fiber epoxy composites at room temperature and high temperature

Effects of stitch yarns on interlaminar shear behavior of three-dimensional stitched carbon fiber epoxy composites at room temperature and high temperature

Non-woven textiles for medical implants: mechanical performances improvement.

Non-woven textile has been largely used as medical implant material over the last decades, especially for scaffold manufacturing purpose. This material presents a large surface area-to-volume ratio, which promotes adequate interaction with biological tissues. However, its strength is limited due to the lack of cohesion between the fibers. The goal of the present work was to investigate if a non-woven substrate can be reinforced by embroidery stitching towards strength increase. Non-woven samples were produced from both melt-blowing and electro-spinning techniques, reinforced with a stitching yarn and tested regarding several performances: ultimate tensile strength, burst strength and strength loss after fatigue stress. Several stitching parameters were considered: distance between stitches, number of stitch lines (1, 2 or 3) and line geometry (horizontal H, vertical L, cross X). The performance values obtained after reinforcement were compared with values obtained for control samples. Results bring out that reinforcement can increase the strength by up to 50% for a melt-blown mat and by up to 100% for an electro-spun mat with an X reinforcement pattern. However, after cyclic loading, the reinforcement yarn tends to degrade the ES mat in particular. Moreover, increasing the number of stitches tends to fragilize the mats.

Design and numerical modelling strategy to form Tailored Fibre Placement preforms: Application to the tetrahedral part with orthotropic final configuration

Tailored Fibre Placement (TFP) allows manufacturing net shape preforms with continuously varying orientations and thickness. This additive technology, combined with forming, enables the design of fibre reinforced composite parts with optimized fibre orientations. A new modelling strategy to simulate the forming of thin dry TFP preform without backing material is proposed. The finite element model is based on an embedded element formulation, which assumes the stitching yarn to act as a bond between fibre tows of adjacent layers. Fibre tows are modelled with 2-node beam elements having independent generalized stress stiffnesses. The forming of a tetrahedral shape with orthotropic final configuration is addressed both experimentally and numerically to validate the proposed approach. The tetrahedral shape has a direct industrial application since it corresponds to corner brackets. This study also demonstrates the ability to improve the mechanical properties of engineered part using the hybrid TFP-forming process.

FEM analysis of unit cell using single I-Fiber stitching process

The development and use of composite materials for several manufacturing industries require reliable adhesives and joints. However, the use of composite joints decreases the strength in the z-direction where composite laminates have lower strength. In this way, several methods have been proposed to reinforce CFRP laminates in the z-direction. Based on previous studies, a new technology in the through-thickness reinforcement for composite laminates called I-Fiber stitching process has been introduced, and the development continues under investigation. In the present research, the experimental results obtained from a unit-cell specimen under pull-out load with three different thicknesses and stitched with a single yarn using the I-Fiber stitching process were analyzed using the finite element method. Microscope image analysis was performed to obtain the best approach of the numerical model. Stress distribution of the I-Fiber and interface analysis using cohesive elements were achieved to understand the performance of the single stitch for each unit-cell case. Finally, a failure load comparison was performed between the experiments and the numerical analysis. The results showed the complexity of the I-Fiber shape under different laminate thicknesses and how the fiber volume of the reinforcement can vary along the thickness using the same stitching yarn for all cases.

The tensile properties of weft-knitted biaxial tubular fabrics and reinforced composites

Weft-knitted biaxial tubular (WKBT) fabrics have been infiltrated via a resin film infusion technique to fabricate reinforced composites. To understand the mechanical properties of WKBT fabrics and the reinforced composites, the strength efficiency of insertion yarns and insertion fiber volume fraction are used to evaluate the tensile strength. The tensile properties of WKBT fabrics and the reinforced composites are studied in the 0° and 90° directions. The results show that both have two failure stages. The first stage is the fracture of insertion yarns which provide the main tensile strength, and the second stage is the fracture of stitch yarns which have significant effect on the tensile strength of WKBT fabrics and the reinforced composites. It is observed that the deformation behavior and failure mechanism of WKBT fabric reinforced composites are closely related to the structure of WKBT fabric, which can be used to predict the failure mode and morphology of WKBT fabric reinforced composites.

Experimental and computational assessment of the bending behavior of inflatable drop-stitch fabric panels

This paper details the experimental assessment and nonlinear finite-element analysis of the flexural behavior of inflated drop-stitch panels. Coupon-level fabric tests as well as panel inflation and panel torsion tests were performed to determine the effective orthotropic moduli of the panel fabric skin. Large displacement bending tests were conducted for a range of inflation pressures and two different span-to-depth ratios to assess the significance of these important parameters on panel stiffness and capacity. A novel, nonlinear beam finite-element modeling strategy for predicting the load–deflection behavior of inflatable drop-stitch panels subjected to bending loads is subsequently presented. The underlying Timoshenko beam element incorporates nonlinearity caused by fabric wrinkling, the work done by the internal pressure and its effect on panel stiffness and capacity, and the effect of the drop stitch yarns on panel bending response. Comparisons between model-predicted and measured panel load–displacement response demonstrate that the model is capable of predicting both pre- and post-wrinkling panel bending behavior over a wide range of deflections with reasonable accuracy. Additional model simulations demonstrate the significant impact of pressure–volume work, shear deformations, and drop yarns on panel bending response.

Characterization of microcracking of NCF composites under accelerated hygrothermal cycles: Influence of the stitching yarn and the style of biaxial NCF

In this paper, an analysis of the evolution of microcracking of Non-Crimp Fabric (NCF) polymer matrix laminates under hygrothermal loading is presented. These composites are reinforced with biaxial NCF styles ([+45/-45], [0/90], etc.) and manufactured by Liquid Resin Infusion (LRI). The samples are subjected to accelerated hygrothermal cycles that cause microcracks in specific resin-rich areas (RRA). Three types of microcracks were found to occur in the heterogeneous morphology of NCF. An experimental method based on 2D microscopic observations was adapted for the characterization of microcracking in several NCF laminates. 3D tomographic X–ray observations were performed to investigate the propagation and location of microcracks in the NCF volume. The influence of humidity on microcracking was investigated. The impact of several parameters on microcracking was discussed, in particular the stitching yarn size and styles of biaxial NCF used in laminates.

Experimental, analytical and numerical investigation on tensile behavior of twisted fiber yarns

Stitched composite materials are emerging as a promising material due to their high interlaminar strength, combined performance and light weight. The mechanical properties of stitch yarns are very essential for stitched composite structures. In this study, the tensile behaviors of the twisted fiber yarn in stitched composites were investigated experimentally, analytically and numerically. Two kinds of cross-sectional area of twisted yarn are proposed and discussed. The paper presents an intersecting circle model to describe the cross-section of twisted fiber yarns, and a physics-based theoretical model to predict the effective tensile moduli. The numerical models take into account the cross-sectional characteristic and the twist architecture. The investigation shows that: the sum of each fiber area should be used for experimental analysis; and the cross-sectional area surrounded by the yarn profile should be used for theoretical predictions and finite element (FE) simulations. The relative errors of the prediction method and the FE simulation are less than 2% and 1%, respectively. The friction between the fibers is derived, and the effect of friction on mechanical properties is discussed. The investigation method will serve as a fundamental component of twisted fiber bundle/yarn analysis.

Study of Compaction Properties and Permeability Prediction of Multilayered Quadriaxial Non-Crimp Fabric in Liquid Composite Molding Process.

A systematic experimental study was performed to detect the compaction and permeability properties of multilayered biaxial and quadriaxial preforms under vacuum pressure. Compression response on ply level showed that the degree of nesting between quadriaxial NCF was more pronounced and the nesting deformation mechanism was affected by the interaction with stitch yarns. Owing to the meso-channels in the fibrous structure and the nesting between layers, the in-plane permeability of quadriaxial NCF did not follow an inverse proportion relationship with the fiber volume fraction. To predict the in-plane permeability of multilayered quadriaxial NCFs, unit cell models at a high level of geometrical details were built, including local variations in yarn cross-sections and the nesting deformation between layers. Numerical methods were implemented, and the prediction results were in very good agreement with the experimental data. Besides, the major contributing parameters to the enhancement of the in-plane permeabilities were identified by investigating the correlation between permeability and structural parameters of quadriaxial NCF. The modeling methodology and the principles established can be applied to the design of the quadriaxial NCF fabrics, where the permeability enhancement was evidenced.