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Three-dimensional simulation of warp knitted structures based on geometric unit cell of loop yarns
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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.
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Virtual fitting technology is widely used in many fields, such as e-commerce, garment computer-aided design, and film and game production. Cloth modeling and simulation play an important role in virtual fitting. The realism and simulation speed directly affect the user experience and visual appearance. This paper first reviews the history of cloth modeling and simulation methods. Then, it focuses on four perspectives: yarn-structure modeling of the cloth modeling level; multi-resolution grid simulation; the relation between human posture and cloth deformation; and collision problems of the cloth simulation level. Yarn-structure modeling considers a unit cell that incorporates the physical characteristics of the fabric and the fabric structure. A multi-resolution grid can integrate techniques from different research fields and may achieve a breakthrough in cloth modeling. Generative adversarial networks (GANs) have potential for dealing with the relation between human posture and cloth deformation by comparing several typical algorithms with GANs. Solving the collision and friction problem depends on choosing the right envelope box for refining the human body surface. Finally, the paper concludes with an analysis of future research trends that could improve the fidelity and speed of a simulation. The paper may serve as a reference for research into cloth modeling and simulation for virtual fitting.
Joints are the weakest links in the composite pipes under internal pressure due to the discontinuity of reinforcement in connection area. Weft-knitted integrated preforms can be used to enhance the strength of these composite joints. The focus of this study is to develop a geometrical model for the finite element analysis of composite joints reinforced with single jersey weft knitted fabric, which take cylindrical forms. Thus our efforts are concentrated on generating geometrical models for weft-knitted integrated preforms as reinforcement of Tee-joint, and various Wye-joint composites in pipelines. A geometrical model was first developed for loops on the curved surfaces by modifying the offered model for loops on flat surfaces. Then, the joint was divided into two cylinders; main cylinder and joint. Each cylinder was modeled using the generated model for loops on curved surfaces. The modeled cylinders were assembled according to the structure of joints. A python algorithm was proposed to simulate the weft-knitted integrated preforms in Abaqus/CAE 2016 commercial package. By implementing the proposed algorithm, the geometry of reinforcement was modeled for three types of joints based on technical data of ASME-B31. To verify the generated model, T-shape weft knitted integrated preform was produced using glass yarn count of 220 tex, CPC and WPC of 6 and 4, respectively. Comparing the experiment and simulation results shows a maximum error percentage of 10 % in the predicting the structural parameters of joints. It can be concluded that the generated model can well predict the geometry of weft-knitted preforms.
Three-dimensionally (3D) knitted technical textiles are spreading into industrial applications, since their geometric, structural and functional performance can be tailored and optimized on fibre-, yarn- and fabric levels by customizing yarn materials, knit patterns and geometric shapes. The ability to simulate their complex mechanical behaviour is thus an essential ingredient in the development of a digital workflow for optimal design and manufacture of 3D knitted textiles. Here, we present a multi-scale modelling and simulation framework for the prediction of the nonlinear orthotropic mechanical behaviour of single jersey knitted textiles and its experimental validation. On the meso-scale, representative volume elements (RVEs) of the fabric are modelled as single, interlocked yarn loops and their mechanical deformation behaviour is homogenized using periodic boundary conditions. Yarns are modelled as nonlinear 3D beam elements and numerically discretized using an isogeometric collocation method, where a frictional contact formulation is used to model inter-yarn interactions. On the macro-scale, fabrics are modelled as membrane elements with nonlinear orthotropic material behaviour, which is parameterized by a response surface constitutive model obtained from the meso-scale homogenization. The input parameters of the yarn-level simulation, i.e., mechanical properties of yarns and geometric dimensions of yarn loops in the fabrics, are determined experimentally and subsequent meso- and macro-scale simulation results are evaluated against reference results and mechanical tests of knitted fabric samples. Good agreement between computational predictions and experimental results is achieved for samples with varying stitch values, thus validating our novel computational approach combining efficient meso-scale simulation using 3D beam modelling of yarns with numerical homogenization and nonlinear orthotropic response surface constitutive modelling on the macro-scale.
In this paper, the filtering effect on fine particle of warp-knitted mesh fabrics was investigated. Polyester yarn (PET) and polyvinylidene fluoride (PVDF) fiber were used as materials to knit the fabrics with five different structures on KS4 tricot warp-knitted machine. After knitting, the fabrics were treated with tourmaline liquid with five different concentrations of tourmaline. Then, the filtration efficiency of samples was tested by the comprehensive test machine. By comparing the filtration efficiency of samples with different concentrations of tourmaline and different structures, the optimal process parameters were obtained that the concentration of tourmaline liquid was 30% and the structure of fabric was one by two insertion. The experimental data of the comprehensive test also revealed that the application of the PVDF and tourmaline did have effects on the promotion of the filtration performance of the warp-knitted fabrics.
The study focuses on effect of twist multiplier on single jersey and 1 × 1 rib knitted fabrics loop length, loop shape, and tightness factors properties. For the study 100% cotton fiber which is processed into 40Ne (English count) carded ring spun yarn is used. Three twist levels of 900 turns/m, 1050 turns/m, and 1200 turns/m with respective twist multipliers of 3.6, 4.2, and 4.8 are used. The single jersey produced from the three twist multipliers is named as Sj1 which is produced from 3.6, Sj2 from 4.2, and Sj3 from 4.8. Similarly, 1 × 1 rib is denoted as R1 which is produced from 3.6, R2 from 4.2, and R3 from 4.8. The test was performed as per ASTM D1776-Practice for Conditioning Textiles for Testing. The tests done for ten specimens and the results showed that loop length, loop shape, and tightness factors properties of single jersey and 1 × 1 rib knitted fabrics are significantly influenced by twist multipliers variation.
In order to create realistic loop primitives suitable for the fast computer-aided design (CAD) of the flat knitted fabric, we have a research on the geometric model of the loop as well as the variation of the loop surface. Establish the texture variation model based on the changing process from the normal yarn to loop that provides the realistic texture of the simulative loop. Then optimize the simulative loop based on illumination variation. This paper develops the computer program with the optimization algorithm and achieves the loop simulation of different yarns to verify the feasibility of the proposed algorithm. Our work provides a fast CAD of the flat knitted fabric with loop simulation, and it is not only more realistic but also material adjustable. Meanwhile it also provides theoretical value for the flat knitted fabric computer simulation.
A parameterized unit cell model of uniaxial reinforced warp‐knitted composites is established through Python programs. The knitting yarns in tricot organization and the Stich Yarn induced fiber Distortions (SYDs) are considered in the model. The phenomenon of uneven fiber content around the SYD areas is described using a hierarchical multiscale model. Longitudinal tensile experiments are performed on this material, and the results are consistent with the numerical prediction. The initial damage is mainly caused by the fiber fracture near the SYD areas, and the matrix between reinforcing yarns tends to crack along the fiber direction. The binding function of knitting yarns in the manufacturing process is highlighted through a failure mechanism comparison with the traditional uniaxial reinforced composites. The parameter analysis indicates that the content of knitting yarns has negative effects on the tensile properties of the material. In addition, the layer thickness has a positive effect on the longitudinal tensile stiffness and strength. These findings can be valuable guides for structural design and manufacture of warp‐knitted composites. POLYM. COMPOS., 2018.
The finite element analysis method (FEM), for its advantages of lower time and economic costing in predicting the mechanical properties of fabrics, was applied to warp-knitted fabrics. In this paper, two bar warp-knitted fabric knitted with wires was used as reflecting mesh antennas. Firstly the loop unit of the metallic warp-knitted fabric was simulated in 3-D by TexGen software. Secondly the 3-D loop unit model was inputted into ABAQUS software to form a model of the metallic warp-knitted fabric sheet for uni-axial tension analysis. Thirdly numerical results were obtained after setting the parameters in ABAQUS. Finally numerical results were verified by uni-axial tensile experiments on the metallic warp-knitted fabric. The results showed that the simulation was in good agreement with the experimental tensile process, where the transfer of yarns between loops when in low fabric elongation and in yarn elongation when in high fabric elongation were simulated by FEM of warp-knitted fabric in the tensile process. Also the same trend of tensile force was found in experiment and FEM results. Therefore it can be concluded that FEM can be used to predict the mechanical properties of warp-knitted fabric with a complex structure. © 2018, Institute of Biopolymers and Chemical Fibres. All rights reserved.
The purpose of this study is to develop a parametric 3-D loop model for warp-knitted structures which can predict loop geometry with variation of process parameters. Firstly, a process matrix of warp-knitted structure and a matrix including 3-D coordinates of date points were, respectively, developed. Then, based on internal stress analysis, an algorithm were suggested which can calculate the process parameter into 3-D coordinates of date points in geometric model of warp-knitted loop. Moreover, loop model were improved by space curve fitting based on piecewise cubic Hermite interpolating polynomial (CHIP). Furthermore, the developed parametric loop model was programmed with software of Matlab2014, and four test samples with different process parameters were simulated. The accuracy of the proposed model was verified by between simulations and micrographs, as well as agreement between predicted run-in values and the measured ones. It is confirmed that 3-D geometry of warp-knitted loop can be well predicted by the proposed parametric loop model.
The paper reports the construction of a warp-knitting machine for spatial knitted fabrics and a dynamic model of its basic working unit – the arrangement of a whip roller and a slider with a guide needle bar. The concept of the machine is based on a positive feeding of the knitting zone, with a little correction from the warp tension, and a rectilinear movement of the guide needle bars by using pneumatic drive. The paper also presents the results of dynamic analysis of the system movement. The influence of the dynamic parameters of the whip roller on the possibility of executing a work cycle with a certain efficiency has been determined. Dynamic load of the warp thread during the cycle is also tested. For the analyzed structure of the machine it has been established that the duration of a single cycle cannot be shorter than 0.2 s. © 2017, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.
A loop-linked structure, which is capable of morphing in various modes, including volumetric transformation, is developed based on knitting methods. Morphing flowers (a lily-like, a daffodil-like, gamopetalous, and a calla-like flower) are fabricated using loop patterning, and their blooming motion is demonstrated by controlling a current that selectively actuates the flowers petals.
In order to predict the appearance and porosity of the metallic two-bar warp-knitted mesh, a three-dimensional (3-D) loop model was developed by some key points on loop, and then based on the model meso structure of mesh was simulated. Firstly, a two-dimensional (2-D) loop geometry in metallic warp-knitted mesh was established. The loop geometry was described on the basis of the yarn property effect to loop sharp. And the underlap geometry was taken as an arc. To describe the 2-D loop geometry, coordinates of key points called databases were established. Then databases in 2-D loop geometry were relocated through the loop offset by stress distribution. Secondly, the 3-D loop geometry was ensured according to the yarn diameter, the angle between loop plane and fabric plane as well as the type of loops (front bar loop or back bar loop), etc. Finally, the coordinates of databases were imported to TexGen software to simulate the 3-D meso structures of the metallic mesh. By comparing simulation images with actual fabrics, the 3-D loop geometry model was fitted well for metallic two-bar warp-knitted mesh. And the simulation results demonstrated that the predicted porosity of mesh was in good agreement with experimental values.