Warp-knitted Fabrics Research Articles

Methodology for Calculating the Consumption of Raw Materials for Complex Structures and Refueling of Warp-Knitted Fabrics

В работе представлена методика расчета расхода сырья по видам использованных нитей при вязании ушковыми гребенками разных переплетений и образованием сложных структур трикотажных основовязаных полотен, а также определение длины заправляемой нити в каждую ушковину соответствующей гребенки.

The friction and wear behaviors of self-lubricating composites with two types of warp-knitted fabric structures

Replacing the traditional self-lubricating fabric composites with new type of wear-resistant composite reinforced by warp-knitted fabrics PTFE-Nomex and PTFE-Nomex/Nomex (self-lubricating fiber: PTFE, reinforcing fiber: Nomex), in which the hybrid graphite/graphene particle modified phenolic is used as the adhesive resin. The influence of the fabric structure on the friction and wear properties of self-lubricating fabric composites was evaluated by the ball-on-disk and bearing friction tests. And the wear mechanism of the composites was investigated through scanning electron microscopy (SEM) and mechanical tests. The ball-on-disk friction test shows that the friction and wear properties of two kinds of composites with different structures are different with the increase of friction distance. In addition, the self-lubricating warp-knitted composite materials were prepared as self-lubricating joint bearing liners to evaluate the bearing application. It is proposed that the wear resistance of the two kinds of warp-knitted composites is poor, and the single layer is slightly better. It is related to the friction mode, mechanical and bonding properties of the bearing liners.

Design of Powernet Knitted Fabrics from PET/BaTiO3 as Pressure Garments for Rehabilitation of Cerebral Palsy

In this study, powernet warp-knit fabrics were designed using polyethylene terephthalate (PET) yarns melt-spun with three different amounts (20, 25, and 30 wt.%) of barium titanate (BaTiO3) and 30 wt.% elastane yarns. The resulting fabrics were characterized by antimicrobial activity cytotoxicity electromagnetic shielding properties, differential scanning calorimetry (DSC) analyses, stiffness tests at MD and CD (machine and cross directions), and pressure measurements using wireless pressure sensors. According to the results, the newly-designed pressure garments would help in the rehabilitation of cerebral palsy patients to improve motor skills and to prevent complications by training muscles with the needed tight structure and electric stimulus onto limbs. They would also provide a hygienic environment during long physical therapy for future designs.

Introduction and Optimization of a Novel Nonlinear Model for the Free Vibration of Warp-knitted Spacer Fabrics

The aim of this study is to present a nonlinear model that can describe the free vibration damping behavior of 3D knitted fabrics. A fabric is considered as a single degree of freedom model which consists of a nonlinear spring paralleled with a dashpot both in series with a mass. The differential equations of the system motion are solved using the multiple scales method. Damped frequency ωd and damping coefficient $$\widehat\mu $$ are determined using the approximate analytical method, the Imperialistic Competitive Algorithm (ICA) and linear methods to estimate the system response. The obtained system response is then compared with experimental results. The results of the study show that, in comparison with analytical solutions and linear models, ICA can predict the behavior of spacer fabrics more accurately. It is also found that the difference between experimental and predicted models is explained by errors of 8.3 %, 13.7 % and 16.2 % for ICA, approximate analytical and linear model respectively.

Compression after Impact and Charpy Impact Characterizations of Glass Fiber/Epoxy/MWCNT Composites

In this study, glass fiber/epoxy resin/multi-walled carbon nanotubes (MWCNTs) were used to fabricate hybrid composites with biaxial warp-knitted fabrics. The biaxial warp-knitted fabrics were grafted with various amounts of MWCNTs and the hybrid composites were fabricated using the resin transfer molding (RTM) method, subsequently. The fabricated samples were subjected to compression after impact and Charpy impact tests. The hybrid composites exhibited higher compression after impact modulus and strength with 26 % and 17 % compared to the samples without nanotubes, respectively. Moreover, the MWCNTs integrated specimens showed 17 % improvement of Charpy impact strength against specimens without carbon nanotubes in 0 ° degree direction. Fracture surface analysis revealed lower number of cracks and shorter crack propagation lengths in the MWCNTs reinforced specimens. The improvement in mechanical properties of the hybrid composites can most likely be attributed to an increase in interfacial adhesion due to the presence of the carbon nanotubes.

A shortened development process method for warp-knitted yarn-dyed shirt fabric

At present, warp-knitted yarn-dyed shirt fabric has become the research focus due to its comfort and highly efficient production. In order to shorten the development process of warp-knitted yarn-dyed shirt fabric, a computing method including theoretical modeling and simulation is proposed in this paper to simulate 2–5 guide bar warp-knitted yarn-dyed shirt fabric. Based on the structure model of warp-knitted fabric, a new model of geometric shape, including loops and underlap, is built according to size measurement results of the loops. In terms of the establishment of mathematical models, such as models of yarn-pressing, loop types, loop locations, guide bar threading, color and fineness, the transformation between knitting technology and mathematical language is realized. With the double buffer technique of HTML (Hypertext Markup Language), loops and underlaps of each bar are displayed separately on different canvases superposed in some order. Simulation is implemented for 2–5 bar warp-knitted yarn-dyed shirt fabric via JavaScript and C# programming languages. The results indicate that this method is able to simulate diverse 2–5 bar warp-knitted yarn-dyed shirt fabrics in a short time. The pattern effect can be seen with a high similarity and practicability before it is produced, thereby shortening the development.

Changeover Process Assessment of Warp-Knitting Let-Off Equipped with Multispeed Electronic Let-Off System

Abstract Warp-knitted fabrics have gained increasing attention due to their excellent properties, and their production is strongly dependent on the warp-based electronic let-off system. Most of the existing control systems are single speed electron let-off structure, which brings a series of issues such as broken yarn, missed needle, and running thread caused by let-off delay, making it hard for manufacturer to produce the required fabrics. To fill the gap, this article proposes a new framework of a multispeed electronic let-off system for warp knitting based on closed-loop control strategy. As a demonstration of the capacity and generalizability of this newly proposed methodology, the 01-type four-channel acoustic vibration analyzer is used to test and analyze the time of switching, the let-off amounts, and the change in warp tension during the process of switching let-off amounts, including the explanation and comparison of difference values of let-off quantities. It is shown that the proposed method for the production of warp-knitted fabrics is a useful method for achieving digital manufacture of warp-knitted fabrics.

Experimental and CFD Analysis of Air Permeability of Warp-knitted Structures

Functionality of technical textiles and apparels in a wide spectrum of end-uses is intensely dominated by their air permeability, which in turn depends on fabric porosity and structure. This work aims to investigate air permeability of warp-knitted fabrics using experimental and numerical simulation methods. Samples of locknit, three-needle satin and four-needle satin two-bar warp-knitted fabrics at tight, medium and loose densities together with single-bar 1×1 and 2×1 warp-knitted fabrics were knitted. The effect of loop density, underlap length and fabric structure on air permeability was investigated. The 3D geometry of locknit and single-bar 1×1 and 2×1 warp-knitted fabrics was modeled using CATIA. The structural geometry of a knitted loop as the unit cell of warp-knitted fabrics was simulated based on Vassiliadis model. The geometry models then were coupled with a computational fluid dynamics (CFD) model for flow simulation. Fluid flow through the fabric structure was simulated by numerically solving incompressible creeping Newtonian flow through the pore space of generated knitted structures using Fluent. The results were then compared with experimental data. It was found that 1×1 single-bar fabrics have higher air permeability than 2×1 single-bar fabrics. It was also found that single-bar fabrics show significantly higher air permeability compared to two-bar warp-knitted fabrics. For the two-bar fabrics, the results point to higher air permeability of locknit fabrics, followed by three-needle satin and four-needle satin. The results also indicated that increase in underlap length and loop density leads to reduction of both pore size and fabric porosity and therefore decreasing air permeability. It was found that the experimental and numerical results are acceptability compatible with error of less than 16 %. It was concluded that the proposed model is potentially capable of prediction of air permeability of single-bar and two-bar warp-knitted fabrics.

Three-dimensional simulation of warp knitted structures based on geometric unit cell of loop yarns

Warp knitted fabrics are typically three-dimensional (3D) structures, and their design is strongly dependent on the structural simulation. Most of existing simulation methods are only capable of two-dimensional (2D) modeling, which lacks perceptual realism and cannot show design defects, making it hard for manufacturers to produce the required fabrics. The few existing methods capable of 3D structural simulation are computationally demanding and therefore can only run on powerful computers, which makes it hard to utilize online platforms (e.g. clouds, mobile devices, etc.) for simulation and design communication. To fill the gap, a novel, lightweight and agile geometric representation of warp knitting loops is proposed to establish a new framework of 3D simulation of complex warp knitted structures. Further, the new representation has great simplicity, flexibility and versatility and is used to build high-level models in representing the 3D structures of warp knitted fabrics with complex topologies. Simulations of a variety of warp knitted fabrics are presented to demonstrate the capacity and generalizability of this newly proposed methodology. It has also been used in virtual design of warp knitted fabrics in wireless mobile devices for digital manufacture and provides a functional reference model based on this simplified unit cell of warp knitted loops to simulate more realistic 3D warp knitted fabrics.

Finite element analyses of auxetic warp-knitted fabric deformation behaviors under low-velocity impact loading

This paper reports the tensile and impact deformation behavior of an auxetic warp-knitted fabric by using the finite element method. The geometrical model of the fabric was obtained from experimental fabric. Tensile and impact deformation behaviors of different auxetic geometrical models were simulated based on the Abaqus software. The finite element (FE) analysis showed that the FE simulation could well predict the tensile and impact behaviors of the auxetic fabric. The auxetic effect of auxetic fabric structural model is related to the angle θ and the long/short rib ratios. The impact resistance of auxetic fabric structural model is also related to angle θ and impact velocity; however it is nothing to do with the long/short rib ratios.

Experimental investigation on shear properties of warp-knitted brush fabrics

Warp-knitted brush fabrics are composed of an outer surface formed by weaving the front and rear needle beds with spacer yarns interposed between them. Warp-knitted brush fabrics can be used as a non-slip cover for car seat cushions; the adhesion between non-slip fabric and car seat is related to the shear strength of warp-knitted brush fabrics. In this article, to study the factors affecting the shear force of warp-knitted brush fabrics, three different processing methods and four different stretching speed intervals were used to find the effects of stiffeners and action of different speed intervals on shear properties of fabrics. The experimental results show that the stiffener treatment can improve the shear resistance of the warp-knitted brush fabrics, and the effect of different speed intervals can affect the shear resistance of fabrics. These findings will have a guiding significance in the design and production of warp-knitted brush fabrics applied to fabrics such as car seat cushions, and the results can also help to study the shear properties of warp-knitted brush fabrics for wider applications.

Study on the NCO index and base knitted fabric substrates on the thermal, chemical, and mechanical properties of solvent-less formulations polyurethane artificial leather

In this article, we have studied the thermal, chemical, and mechanical properties of the polyurethane artificial leather. Polyurethane artificial leathers were made from polyol, diisocyanate, chain extender, a catalyst, polyester circular knitted fabric, and warp knitted fabric. After manufacturing the artificial leathers, the properties of six different samples were investigated according to the NCO index. The equivalence ratios of the isocyanates to polyols containing a hydroxyl group are referred to as the NCO index. Samples were synthesized with an NCO index of 1.0, 1.4, and 1.8 by changing the weight ratio of diisocyanate. The result showed that as the NCO index increased, the unreacted NCO functional groups and cross-link increased and the mechanical properties of the polyurethane artificial leather were increased. The mechanical properties of circular knitted fabric polyurethane artificial leather were superior than warp knitted fabric polyurethane artificial leather.

An experimental investigation for the temperature effect on the bending properties of multiaxial warp-knitted composite

An experimental study of bending properties of composites reinforced with triaxial and quadaxial warp-knitted glass fabrics was carried out in the 0°, 45°, and 90° directions at −30°C, 0°C, 20°C, and 40°C, respectively. The relationships between the stress–strain curves, bending strength, bending modulus, and temperature were obtained. The failure mechanisms at different temperatures were also analyzed based on the fracture morphologies and scanning electron microscope (SEM) images. The results indicated that the bending properties decrease slightly with the increase in temperature from −30°C to 20°C and decrease dramatically from 20°C to 40°C. The ultimate bending strength of triaxial and quadaxial warp-knitted composites decreases approximately 31.34% and 34.29%, respectively. In particular, the relationships between bending strength and temperature were also obtained by nonlinear fitting with the experimental data, which could be used to predict the bending behavior at different temperatures.

Low-velocity impact behavior of intralayer hybrid composites based on carbon and glass non-crimp fabric

The low-velocity impact behavior of intralayer hybrid composite laminates made from warp-knitted fabrics with carbon (C) and glass (G) fibers was investigated. The impact testing at varying energy levels was performed using drop weight impact tests. The impact response was evaluated in terms of peak force and absorbed energy, and damage mechanism were characterized by visual observations and fluorescent dye penetration. Furthermore, the damage modes was assessed through quasi-static indentation (QSI) and acoustic emission (AE) techniques. The results from this study indicated that the hybrid structure exhibited a positive hybrid effect in peak force and the absorbed energy, and failure mechanism were significantly affected by the hybrid ratio and intralayer structure. The intralayer hybrid laminate of C:G = 1:1 revealed better impact resistance, and that of C:G = 1:4 exhibited less damage accompanied by the least carbon fiber content, however, more fiber damage appeared in C:G = 1:2 laminates.

Study of Flexural Behaviour of Warp Knitted Reinforced Ferrocement Composites

This paper presents the effect of warp knit textile reinforcement in ferrocement laminates. In general, steel wire mesh is used as ferrocement reinforcement, which is often known as chicken mesh. The need for the replacement of steel mesh is the problem of corrosion, which reduces the durability of ferrocement laminate. High performance synthetic fibres and fabrics are constantly used in various research works as reinforcement in concrete. In this paper, an attempt was made to incorporate three different nylon warp knit mesh structures in the place of chicken mesh. Ferrocement composites were produced with chicken mesh and nylon warp knit fabrics. The flexural properties of ferrocement laminates were analysed in terms of the first crack load, ultimate load, energy absorption capacity and ductility factor. Nylon square mesh with 3 layers in the reinforcement has a 2.5 kN first crack load and 3.36 kN ultimate load, which is higher than chicken mesh reinforcement in ferrocement laminate. The results show that there is an improvement in the flexural properties of ferrocement laminates reinforced with a nylon warp knit structure. The flexural parameters have a direct relationship with the number of layers used in the reinforcement.

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

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.

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

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.

Calculation and Analysis of Horizontal and Vertical Lapping Angles in Tricot Warp Knitting

Abstract The lapping angle, which affects the style and quality of production, has been studied as a parameter of weft knitting. But the importance of the lapping angle has not been considered during the warp-knitting cycle. This paper shows that the lapping angle exists in the process of warp knitting and can be divided into horizontal and vertical lapping angles. Models for the lapping angles of closed and open loops were devised, and the lapping angles (horizontal and vertical lapping angles) of closed and open loops were calculated and analyzed. Furthermore, the paper seeks to investigate the factors that influence the lapping angle of tricot warp-knitted fabrics and summarize the rules. Moreover, the vertical lapping angle can affect the loop coverage. Results reveal that the decrease in number of underlaps and an increase in take-off density enables loops of the front guide bar to show on the face of the fabric. Moreover, it is also advantageous for an apparent front loop visibility when the front guide bar knits in open loop.

Manufacture and Property of Warp-Knitted Fabrics with Polylactic Acid Multifilament.

This study investigates the properties of polylactic acid (PLA) multifilament and its warp-knitted fabrics. Multifilament properties were tested and compared with PET multifilament with different diameters. The 83.3 dtex PLA multifilament was used to knit the fabric, and the fabric properties before and after dyeing were studied. Results showed that the mechanical properties of PLA multifilament were comparable to those of PET. However, PLA had a higher heat shrinkage rate. The dyed PLA warp-knitted fabric has excellent color fastness. Due to the influence of temperature and dye particles during the dyeing process, the breaking strength, air permeability and moisture permeability of the fabric were decreased. On the contrary, the elongation at break, abrasion resistance, anti-pilling properties, drape and crochet value of the fabric were increased.

Mesoscale model for elastic modulus of warp-knitted fabric-reinforced composites based on spring model

In this paper, a ‘mesoscale spring model’ was generated to predict the tensile modulus of warp-knitted fabric-reinforced composites. A previously developed geometrical model was used for generating a mechanical model as a set of series and parallel springs. For this purpose, the unit cell of straight line model was discretized into different segments. Each segment was modelled as a spring with definite constant based on the alignment of yarns in the segment. Warp-knitted fabrics (Queen's Cord) were used as reinforcement of composites. In order to validate the presented model, samples of composites were produced using hand layup method. Tensile tests were carried out on the prepared samples. The comparison between theoretical and experimental elastic modulus showed a reasonable agreement between experimental and theoretical data. Also, the comparison between the results of different models and experimental data showed that the results of spring model are closer to the experimental results than that of Krenchel's model. It can be concluded that the spring model can predict adequately the elastic modulus of composites.