Double Needle Bar Research Articles

Three-dimensional simulation based on mesh modelling for warp-knitted fully-formed garments

PurposeThe warp-knitted fully-formed shorts are one kind of fully-formed garments knitted by a double-needle bar machine, which is widely used in the medical field. Because of its distinctive forming method, designers are unable to grasp the final effect of the product accurately during the design process. The purpose of this paper is to clarify a visible 3D simulation method in the design process along with the knitting method and structure characteristics, which is reflected in the final product effect.Design/methodology/approachThis study introduces a simulation process for warp-knitted fully-formed fabric from an input 3D surface model group. Stitch mesh models are established according to the garment structure and the triangle index of the garment model that swchape-controlling points belong to is calculated. The garment model group includes a 2D plate and a 3D model, between which there is a space coordinate transformation relationship. The study makes use of the 3D tubes to connect the coordinate points in order and render the tubes in real yarn colors. The effects of two parameters, radial segment and tubular segment, are analyzed and decided to obtain a fine surface within a reasonable rendering time.FindingsA stereoscopic simulation process from flat fabric to 3D product is realized using computer graphics technology. The warp-knitted fully-formed short is shown during the design process within a short time by setting the rendering parameters of tubular segments (ts = 125) and radial segments (rs = 6).Originality/valueVisual simulation for the shorts provides a time-saving and resource-saving method for structure design and parameter modification before knitting. There is no need to knit samples repeatedly to satisfy demand, which indicates that it is a saver of time and resources.

Warp knitted spacer microfiber biomass carrier for wastewater treatment

The development of novel biomass carriers is an option for increasing the efficiency of processes at wastewater treatment plants (WWTPs). Biomass carriers support the adhesion of specific bacteria and the subsequent biofilm formation. As part of this work, a new type of microfibrous biomass carrier with a unique sandwich structure was developed. Technologically, the structure of the biomass carrier is based on warp knitted spacer fabric created on a double-needle bar machine. Commercially available microfiber materials were used to achieve a large specific surface area (SSA) and internal porosity of the carrier to ensure high microorganism capture. A yarn combination was chosen to reach a final carrier density slightly lower than water to float in an aqueous environment. As the first, was developed and described a three-dimensional warp knitted microfiber biomass carrier. Next, were evaluated the properties of this carrier for post nitrification on WWTPs and compared with commercially available biomass carriers. Testing biofilm (using respirometry, real-time polymerase chain reaction, and next-generation sequencing) growing on the developed carrier in a post-nitrification laboratory reactor showed excellent adhesion, stability, and abundance of microorganisms. A high rate (more than 95%) of ammonia nitrogen removal was achieved in post-nitrification, and molecular genetics methods confirmed the high concentration of nitrifying bacteria in the biofilm. The developed three-dimensional microfiber biomass carriers have proven their functionality and can be considered an advance in biofilm processes.

Design and manufacture of three-dimensional auxetic warp-knitted spacer fabrics based on re-entrant and rotating geometries

Warp knitting technology is a fabric-forming technologies that is very suitable to fabricate three-dimensional (3D) auxetic fabrics due to its high efficiency and powerful pattern designing possibilities. In this study, two typical auxetic geometries, namely the re-entrant hexagonal network and rotating square solids, were selected as the design prototypes for the design and manufacture of 3D warp-knitted spacer fabrics. While two 3D warp-knitted spacer fabric structures with representative units of different sizes designed based on the re-entrant hexagonal geometry were manufactured by using a RD7 double needle bar Raschel machine with seven yarn guide bars, two 3D jacquard warp-knitted spacer fabrics with different base fabric structures designed based on the rotating squares geometry were fabricated by using a RDPJ4/2 double needle bar jacquard machine with two ground yarn guide bars and four jacquard guide bars. The Poisson’s ratios of these 3D warp-knitted fabrics in the course direction and wale direction were evaluated respectively through constant-rate tensile tests. The results revealed that the re-entrant hexagonal fabric structure with double chain stitches has auxetic behavior across a wide range of tensile strains along the course direction, while the rotating square fabric structure with elastic chain stitches as the base is auxetic within a narrow range of tensile strains along the wale direction. The study provides an alternative method to directly produce auxetic warp-knitted spacer fabrics through a single knitting process instead of using an additional post-compression and heat-setting process.

Mesh modeling and simulation for three-dimensional warp-knitted tubular fabrics

This article concentrates on a geometric-based simulation method for warp-knitted tubular fabrics. The warp-knitted tubular fabric is unfolded as a two-dimensional flat fabric after analyzing the structural characteristics of this kind of fabric knitted on the double needle bar warp knitting machine. Based on the principle of spatial transformation, a coordinate transformation algorithm using matrix operations is proposed, which allows a two-dimensional flat fabric to convert into a three-dimensional shaped tubular fabric. Spatial positions for data points of every single stitch are confirmed by coordinate mapping to fit the curved surface. Stitches undergo the deformation with the principle of the mass-spring model so as to make the mesh structure appear. Integrated with spatial transformation matrix operations, the validity of the proposed method is experimentally confirmed by simulating the warp-knitted tubular fabrics with the tube diameter changing of different segments, which realize the three-dimensional simulation for vivid shaped warp-knitted tubular products.

Low-velocity impact response of 3D polyurethane resin composites reinforced with spacer fabrics

This research aimed to investigate the low-velocity response of polyurethane-based composites. Three warp-knitted spacer fabrics produced on a double-needle bar warp knitting machine by vary different surface structures were used as the reinforcement element. Two Micro-balloons were added into the composites as well. A new type of resin named polyurethane resin was involved for fabricating the composites. Accordingly, the impact behaviors of composites were evaluated properly under the impact velocity of 1 m/s and 2 m/s, respectively. The findings obtained illustrate that the composites possess excellent low-velocity impact properties and the impact resistance capacities are significantly affected by the fabric surface structures and the types of Micro-balloon, indicating that their impact energy absorbability can be tailored to meet the specific end-use requirements by varying the structural parameters.

Evaluation of the knitted fabrics stiffness through dynamic testing

The paper aims at introducing a qualitative method for the evaluation of warp knitted spacer fabrics stiffness, through the measurement of their natural frequencies, considering the direct relationship between natural frequencies of the textile fabrics and their stiffness. Additionally, the goal of this work was to comparatively evaluate the results obtained by two testing methods that utilise different measurement principles. The experimental design included the free vibration method, employed to measure the natural frequencies of the spacer mesh structures produced on K. Mayer RD 6 N double needle bar machine, manufactured in two variants of thickness and widths.The natural materials frequencies have been recorded coursewise, walewise and perpendicular on the fabric surface. The testing results confirmed the influence of the fabric thickness, the samples having lower thickness being characterized by the highest level of natural frequencies and stiffness. In parallel, the analysis of the knitted spacer fabrics’ flexibility was performed, allowing a comparison of fabrics stiffness and validating the dynamic test results.

Modeling of double-layer jacquard fabrics for pattern simulation

PurposeDouble-jacquard technique is referred as the most advanced technology for forming patterns on both layers of a 3D fabric knitted on a double-needle bar warp-knitting machine. In order to realize the computer-aided design and simulation of jacquard patterns, the purpose of this paper is to propose a mathematic model for representation of jacquard structures and an improved mass-spring model to improve the simulation of structural deformation behavior.Design/methodology/approachPrimarily, it analyzes the jacquard patterning method and displacing principle to design jacquard structures on each layer and linking structures of two layers. Based on that, a loop geometry defined by six key points and segmental lines is built to transfer the jacquard bitmap and lapping movements into a fabric of loops and therefore realizing patterns visualization. Afterwards, an improved mass-spring model is built to simulate structural deformation, in which the fabric is simplified as a mesh of uniformly distributed mass particles. Each loop is treated as a massless particle while underlaps are referred as structural springs connecting loops particles. Elastic forces of these springs on each loop particle is calculated according to the Hook’s law and Newton’s second law, and then based on the explicit Euler’s equations, motion state of each particle is solved including the velocity and the shift.FindingsBased on the above method, a simulator for double-layer jacquard fabrics is developed via Visual C++ language to visualize the patterned fabrics with pitting effects. With a jacquard shoe fabric as an example, this simulation model is proved to be practical and efficient by comparing the simulation result and real fabric.Research limitations/implicationsBecause of limited researches, 3D simulation modeling of this double-layer jacquard fabric will be studied in the further research.Practical implicationsThe implement of this simulation method will offer the industries a time-saving and cost-saving approach for new fabrics development.Originality/valueThis approach can be used as a reference for simulating other knitted fabrics with jacquard patterns, such as jacquard garment fabrics and home textile fabrics.

In-plane shear behavior of 3D warp-knitted spacer fabrics: Part II—Effect of structural parameters

The objective of this work is to study the in-plane shear behavior of 3D warp-knitted spacer knitted fabrics by using a picture frame fixture. This part aims to investigate the effects of structural parameters on the shear stress and energy absorption of warp-knitted spacer fabrics. A group of warp-knitted spacer fabrics was produced on a double-needle bar Raschel machine by varying their structural parameters including spacer yarn fineness, fabric thickness, and outer layer structure. The effects of fabric structural parameters on the shear properties of the spacer fabrics were tested and analyzed based on the nonlinear behavior of shear stress versus shear angle and the deformation mechanism. During loading process, the series of surface images were acquired in certain interval at different positions. These images were processed in image analysis software to obtain the full-field displacement and shear angles at chosen points on the surface of test specimen. The potential shear behavior of the fabric was identified with support of the shear stress–strain curve, work done, and efficiency at different shear stages. The regression model was used to establish the elastic deformation properties to obtain the shear results. Advance statistical evaluation and two-way analysis of variance are used to analyze the significance of various factors such as thickness, spacer yarn diameter, and surface structures on energy absorption at maximum shear load and deformation.

3D simulation model of warp-knitted patterned velvet fabric

Purpose Realistic geometric description is essential for simulating physical properties of warp-knitted velvet fabrics, which are widely used for home-textiles and garments. The purpose of this paper is to provide an approach to the description of patterned piles and propose a customized simulation model to realize highly real-time simulation of warp-knitted velvet fabrics in three dimensions. Design/methodology/approach Based on knitting technology and structure features, a mathematical model to qualify forming possibility of piles is conducted by assessing underlaps of pattern bars and pile ground bars. When the pile areas and ground areas are classified, a three-dimensional (3D) space coordinate is built, of which the z-axis is divided into equal spaces to form certain multi-layer textured slices. Color and transparency of piles on each textured slice can be computed and generated by mapping to 3D geometrical grid layers with particular mapping relationship. Moreover, piles’ deflection and spatial collision are also taken into account to make sure high uniformity with real fabrics. Findings According to the models built, a simulator special for warp-knitted patterned velvet fabrics is programed via Visual C++ and the models are proven practical and easily implemented by comparing simulated effect of one sample with real fabric. Research limitations/implications Because of present limited research, 3D simulation of patterned velvet fabrics knitted on double-needle bar Raschel machine as well as 3D shadow effect will be studied in the further research. Practical implications The paper includes implications for designing patterned velvet products and shows convenience to instantly see finished effect without sampling on machine. Originality/value This paper fulfills a featured simulation method for warp-knitted patterned velvet fabrics in 3D dimensions for the first time.

Protective properties of warp-knitted spacer fabrics under impact in hemispherical form. Part II: effects of structural parameters and lamination

This part aims to investigate the effects of structural parameters and lamination on the impact force attenuation properties of warp-knitted spacer fabrics developed for impact protectors. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel machine by varying their structural parameters including spacer monofilament inclination and fineness, fabric thickness, and outer layer structure. The effects of fabric structural parameters, impact energy levels, and laminated layers on the protective performance of the spacer fabrics were tested and analyzed based on the assessment of the peak transmitted force. The results showed that all the structural parameters significantly affect the impact force attenuation properties of the warp-knitted spacer fabrics. It was also found that lamination of the spacer fabrics can effectively improve the force attenuation performance. Three layers of the developed warp-knitted spacer fabrics in a total thickness of about 2.5 cm can meet the requirement of the transmitted force lower than 35 kN at an impact energy of 50 J according to the European Standard BS EN 1621-1:1998.

Investigation on the impact and compression-after-impact properties of warp-knitted spacer fabrics

The paper reports an experimental study on the influence of spacer fabrics' structures, that is, different surface stitches, fabric thicknesses, and diameters of spacer yarns, on the impact and compression-after-impact properties of warp-knitted spacer fabrics. Low-velocity impact tests, damage deformation characterizations, and compression tests after impacts were performed on six spacer-fabric specimens knitted on a double needle bar Raschel knitting machine. The impact method was flat-sphere (a flat striker contacted with a fabric wrapped on a hemispherical steel anvil). Deformation processes of typical spacer fabrics, force–displacement/time and energy–time curves, impact damage, and residual strength were analyzed and discussed; moreover, peak force, absorbed energy, damage depth, and the drop-off rate of residual strength were involved to estimate impact and compression-after-impact properties of the spacer fabrics with different structures. The results show that with the closed surface structure and coarser spacer yarns, the fabrics have the characteristics of lower peak forces, higher energy-absorption ability, lower damage depths, and higher drop-off rates of residual strength. Fabrics with higher thickness are of the features above but they do have lower drop-off rates

Impact compressive behavior of warp-knitted spacer fabrics for protective applications

This paper presents a study of the impact compressive behavior of warp-knitted spacer fabrics developed for human body protections. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel warp knitting machine by varying their structural parameters, including spacer monofilament inclination and fineness, fabric thickness, and surface layer structure. A drop-weight impact tester was used to test these fabrics with predefined impact energy. The impact process of a typical spacer fabric was analyzed based on its impact contact force-displacement curve, energy absorbed-contact force curve and transmitted force-time curve. The effects of the structural parameters on the impact compressive behavior of the warp-knitted spacer fabrics were also discussed. The relationship between the peak transmitted force and peak contact force was established for these fabrics. The study shows that the warp-knitted spacer fabrics can be used as a type of effective material for human body protection due to their high energy absorption capacity and reduction of the contact peak force. The study also shows that all the structural parameters significantly affect the impact compressive behavior of the warp-knitted spacer fabrics in terms of peak contact force, peak transmitted force, and energy absorbed at different impact compressive stages. According to the results obtained, the warp-knitted spacer fabrics studied can reduce about 33.16% of the peak contact force.

Knitting Crafts and Products Design of the Double-Faced Jacquard Stitch

Jacquard stitch is widely used in clothing and many other areas in recent years. The paper describes the structural features, classification and knitting crafts of the jacquard stitch. Particularly are the knitting process and the locus of needles on the needle bar. However, newly design by the fancy appearance formation regularity is the emphasis of this paper. The design principle is according to the arrangement of color yarns and the drafting of new stitches. Cotton and polyester blended yarns are taken as the raw materials with several colors. Finally, a style of the double-faced jacquard stitch of the complementary yarns and a style of the sesame points are finished on the double-needle bar by the flat knitting machine.

Knitting Crafts and Products Design of the Double-Faced Jacquard Stitch

Jacquard stitch is widely used in clothing and many other areas in recent years. The paper describes the structural features, classification and knitting crafts of the jacquard stitch. Particularly are the knitting process and the locus of needles on the needle bar. However, newly design by the fancy appearance formation regularity is the emphasis of this paper. The design principle is according to the arrangement of color yarns and the drafting of new stitches. Cotton and polyester blended yarns are taken as the raw materials with several colors. Finally, a style of the double-faced jacquard stitch of the complementary yarns and a style of the sesame points are finished on the double-needle bar by the flat knitting machine.

Compression behavior of warp-knitted spacer fabrics for cushioning applications

Cushioning materials generally absorb kinetic mechanical energy under compression actions at a relatively constant stress over a large range of displacement. However, cushioning materials widely used today are polyurethane (PU) foams with low moisture transmission. As a new class of three-dimensional textile structures, warp-knitted spacer fabrics not only have much better moisture transmission property than PU foams, but also have the similar cushioning performance if appropriate structural parameters are adopted. This paper reports an experimental study on the compression behavior of a series of warp-knitted fabrics made for cushioning applications. These fabrics were produced on a double-needle bar warp knitting machine of gauge 18 by varying different structural parameters including spacer yarn inclination angle and fineness, fabric thickness, and outer layer structure. Both the compression stress-strain curves and energy efficiency diagrams from the testing results were used to analyze the compression behavior of these fabrics and the effect of each structural parameter. The results indicate that warp-knitted spacer fabrics are an ideal class of the energy absorbers for cushioning applications and their energy-absorption capacity can easily be tailored to meet specific end-use requirements by simply varying their structural parameters with the help of efficiency diagrams.

3-D Textiles for Advanced Cement Based Matrix Reinforcement

This article gives a definition for the wording 3-D textiles and presents the latest developments in the field of 3-D textile production. The double needle bar raschel technology has been improved by inserting straight reinforcement yarns inserted bi-axially on both sides of the textile. This is a completely new approach and allows a wide range of new applications. One major application of the bi-axially reinforced spacer fabrics is the `textile reinforced concrete' (TRC). In TRC, ready-made textiles can be used instead of single fibers in order to take full advantage of the fiber strength. As the 3-D textiles can be positioned conforming the load situation in three dimensions, they show a superior behavior from technical and economical point of view. A completely new type of 3-D-fabric is presented — warp knitted spacer fabrics for concrete applications.