Yarn Cross-section Research Articles

Investigation of the dynamic compression behavior of 3D braided composites based on a virtual fiber embedding method

The three-dimensional braided composites (3DBCs) possess a complex spatial structure, which can lead to microscopic deformation of fibers under high-speed impact. This paper proposes a quasi-fiber scale model using virtual fiber-embedded (VFE) method to simulate the impact behavior and failure of 3DBCs. The results reveal that the maximum eccentricity of the VFE model yarn cross-section is 0.318, representing a 194% improvement compared to solid yarns. According to the characteristics of damage, it can be deduced that interactions among fibers play a pivotal role in determining the failure behavior of composites, particularly concerning non-linear changes. The modulus, strength and the time of initial damage rise with an increasing braiding angle, whereas the resin stress, yarn stress, and degree of damage exhibit opposite trends. The stress distribution over the braiding path shows that the main load-bearing component at 20° braiding angles is internal yarns, whereas the surface yarns take precedence at 40°. The maximum deformation of the yarn cross-section always occurs at the center of the shear band, with a maximum eccentricity of 0.456 at 20° braiding angles. The deformation in yarn flexing and cross-section flattening cause an uneven distribution of stress and strain, leading to localized damage and ultimately catastrophic destruction.

Experimental and numerical evaluation of the influence of voids on sound absorption behaviors of 3D printed continuous flax fiber reinforced PLA composites

This study aims to quantitatively analyze the effects of voids on sound absorption properties of 3D printed continuous flax fiber reinforced PLA composites (CFFRCs). Three kinds of flax yarns with different linear density were employed to prepare CFFRCs via 3D printing technology. The sound absorption performances of these composites were measured using the impedance tube based on the two-microphone transfer function method. The microstructure morphologies including cross-sections of flax yarns, voids shape and distributions of the composites were observed via ultra-depth microscope and micro-computed tomography to reconstruct the exact structures in simulation. Mercury intrusion porosimetry was applied to measure the voids dimensions of CFFRCs. The influence of voids on sound absorption mechanisms of CFFRCs were revealed based on thermoviscous acoustics theory by conducting the simulation in COMSOL software. The experimental results demonstrated that CFFRCs exhibited excellent sound absorption coefficients (close to 1) within the frequency range of 150–350 Hz and 350–550 Hz, resulting from the voids inside and between the flax yarns respectively. With the increase of linear density (diameter of the yarn), the contents of voids inside and between the flax yarns both increased. The dimensions of voids inside the flax yarns improved while those between flax yarns remained unchanged. The existence of the voids between the flax yarns resulted in a decrease in the sound absorption coefficient of CFFRCs, while more voids inside flax yarns led to the increase of the sound absorption frequency. Numerical results indicated that voids between the flax yarns contributed to a more uniform change in sound speed, reducing sound absorption performance. Whereas, voids inside the flax yarns could improve viscous friction of soundwaves due to narrow structures, enhancing sound absorption capabilities. This study is anticipated to provide a guidance for the design of integration of structure and function of 3D printed CFFRCs.

Automatic reconstruction of closely packed fabric composite RVEs using yarn-level micro-CT images processed by convolutional neural networks (CNNs) and based on physical characteristics

Micro-CT scanning is an advanced technique to reconstruct inner architectures for RVEs of fabric composites. Currently, however, there exist few automatic approaches to separate closely packed yarns in the micro-CT images with economical resolution that can only identify yarns but not individual fibers. To tackle this issue, an innovative method has been developed in this work to identify cross-section area of the yarns via deep-learning-based image segmentation, and then reconstruct 3D geometry model of the composites containing local fiber orientations. The image segmentation was achieved through semantic segmentation by U-Net with validation accuracy of 87 % counted by mIOU and object detection by YOLO v8 with validation accuracy of 99.5 % counted by mAP50. Micro-CT slices with different morphological characteristics were divided into three groups via a ResNet50-based image classification network and selected in ratio to form the training datasets for U-Net and YOLO v8 with high representativity and efficiency. Extraction of individual cross-sections of weft and warp yarns were conducted only using the micro-CT scanning from one angle of view to reduce scanning cost and yarn-to-yarn penetration error. An algorithm considering physical constraints of the yarns was also completed to estimate local fiber orientations with maximum error of 18.065°, nearly 50 % smaller than the existing method.

Predictive modeling of 3D textile composites using realistic micromechanical representations

An innovative and efficient progressive damage model, informed by coupon tests, and using minimal, readily available material parameters, is proposed in this paper to comprehensively predict the tensile, compressive and shear stress–strain response and strengths of a 3D woven angle interlock composite within 5% of test data. Realistic, high-fidelity microgeometries, with process-induced defects, and devoid of geometric assumptions, are constructed using the digital element approach. Excellent correlations with test micrographs are observed for yarn cross-section areas, aspect ratios and crimp ratios, that are on average within 5.5%, 1.9% and 1% of the micrograph measurements respectively. The mesoscale predictions capture the detailed failure mechanisms under each loading condition. Analytical stiffness expressions are derived in terms of the constituent material elastic properties and architecture geometry, which also predict the stiffnesses within 10% error margin. A robust workflow is established that combines the high-fidelity microgeometry generation, automated conformal finite element model creation and comprehensive property prediction capabilities to provide a holistic solution.

Fiber-level modeling of 3D braided preforms using virtual braiding method

High fidelity geometry models of the preforms are essential in mechanical property analysis for composite materials. The paper presents a virtual braiding method to generate digital material twins of 3D braided preforms. The four-step 3D braiding process is simulated based on the concept of virtual fiber and according to the rule of yarn movement. Fiber-level models of the preform are constructed which display the micro-scale architectures explicitly, including compressive deformations of yarn cross-sections and variations of yarn paths. The Micro-CT test is employed to investigate the internal fiber structures of 3D braided preform and quantitatively verify the accuracy of the proposed modeling method. Influence of the braiding parameters, such as yarn tension and arrangement angle in the initial state on geometric parameters of the preform is then investigated.

Effect of stable-structural 3D woven preform on tensile and flexural properties of carbon fiber/epoxy composites

The geometry of yarns effect the structural stability of 3D woven preform, which influence the mechanical properties of carbon fiber/epoxy composites. To investigate the effect of stable-structural preform on the elastic properties of 3D woven composites, the factors that caused the unstable structure of preform were discussed, and comparative study was conducted. The geometric models of yarn cross-section and preform were established to discuss the stability. The results showed that increasing the opening angle of warp yarns and the elongation of yarn outer contour can improve the stability of preform. The tensile and bending tests of 3DLAC and 3DBAC with stable and unstable structural preform were conducted. The results showed that the tensile and flexural elastic moduli were inversely proportional to the curvature of load-bearing yarns, and the elastic modulus of composites with stable-structural preform can increase by 9%–13%. The redistribution of internal stress in composites was macroscopically manifested as stable changes in experimental process. 3D woven composites with stable-structural preform showed the regular fracture cross-section, and fiber fracture and interface adhesion effect were the main failure mode in tensile tests, and fiber fracture on the compression surface and matrix cracking were the main failure modes in bending tests.

Incorporation of compaction effects in the automated generation of 3D woven composites representative volume elements by geometrical modelling

Advanced 3D woven composites have become an enabling technology in many industrial applications due to their proven benefits, particularly the improvement of the out-of-plane mechanical behavior with respect to other reinforcement schemes. The latter property has been shown to be strongly affected by the effects of compaction during manufacturing. The present study proposes an automated framework, based on heuristic procedures, for the generation of representative volume elements (RVEs) of 3D woven composites, allowing to include global and local geometrical features induced by transverse compaction, such as overall thickness reduction, changes in yarn cross-sections and consistent global/local fiber fractions. The methodology is illustrated for three types of reinforcement, namely a plain weave, an angular through-thickness interlock and a 3D orthogonal RVE. The resulting geometries generated by the proposed method compare favourably with typical observations from the literature in a quantitative manner. Finally, the proposed framework is integrated with a previously developed meshing strategy to allow damage studies for a selected architecture (plain weave) under torsional loading, presenting a complete computational chain by building cohesive zone finite element models from compacted RVEs. The torque-angle response curves obtained after the damage simulations show a decrease in stiffness and an increase of damage levels with compaction, which is in line with the expectations.

Investigation into the effect of the blend ratio on the structure and properties of dual-feed-opening rotor-spun yarn

The scope of this study was to investigate the effect of the blend ratio on the structure and properties of dual-feed-opening rotor-spun yarn. A variety of yarns with different blended ratios were spun from two viscose fibers with the same properties but different colors. Through digital image processing technology, the ratios of the area occupied by the two fibers on the surface and the cross-section of the yarns were obtained. The results showed that the yarns with blend ratios of 40/60 and 50/50 had an obvious spacing phenomenon of two fiber segments on the surface. The ratio of the area occupied by the two fibers on the yarn surface was not equal to the value of the blend ratio. In the yarn cross-section, the difference in the area ratio of the two fibers to the blend ratio was subtle. The blend ratio had little effect on the mechanical properties (strength and elongation at break). However, the quantities of hairiness fluctuated greatly. The mass irregularity and imperfections decreased as the blend ratio approached 50/50. This work provides important guiding insights for the research of dual-feed-opening rotor-blended yarn.

Prediction of mechanical properties of 3D tubular braided composites at different temperatures using a multi-scale modeling framework based on micro-CT

It is of great significance to establish a real three-dimensional (3D) tubular braided composites mechanical properties prediction model at different temperatures. In this paper, a multi-scale modeling framework based on micro-computed tomography (micro-CT) is adopted to consider the characteristics of the real yarn cross section, fiber shape deviation and internal defects within the matrix after composite formation, and a realistic trans-scale finite element model for 3D tubular braided composite is established. The micro-scale and macro-scale mechanical properties of 3D tubular braided composites at different temperatures are sequentially simulated by using the elastic-plastic damage model considering temperature and the tractor-separation constitutive model. Comparison with experiments shows that temperature significantly affects the mechanical properties. With the increase of temperature, the overall failure degree of the 3D tubular braided composite under axial compressive load increases significantly, its axial compressive strength and modulus decrease significantly, and the post-peak response of the stress-strain curve gradually flattens. The proposed trans-scale model demonstrates high predictive accuracy.

Transverse compaction of twisted carbon yarns: Experiment and elasto-plastic Mohr–Coulomb modeling

The mechanical characterization of the carbon yarns, the major component of woven textiles for composite materials, is essential for optimizing the fabrication and the final properties of such materials.This work focuses on carbon yarns formed by twisting several elementary tows, each composed of thousands of carbon fibers, whose weak cohesion is ensured by a sizing agent. Different twist magnitudes are studied in dry and wet conditions. Transverse compaction tests are performed with loading–unloading cycles of increasing amplitudes. They have shown that the yarn cross section approaches a critical state where the fiber volume fraction remains constant, irrespective of twist level and humidity.The experimental results evidence an elasto-plastic behavior, analogous to that of a 2D granular medium. A simple model is proposed with a cohesive non-associated Mohr–Coulomb plasticity, having very few constitutive parameters. The effect of twist, water, and sizing can be accounted for.

EXPLORING THE RELATIONSHIP BETWEEN YARN TYPE AND PACKING DENSITY: A STUDY OF SINGLE-PLY, TWO-PLY, AND SIRO-SPUN YARNS

Studying the fiber positioning in the yarn structure is the essential point to understand the different characteristics of yarns that counted as alternatives to each other. This study explores the packing densities of single-ply, two-ply and Siro-spun spun yarns that have been stated as the alternative yarn types considering the production method or yarn structure. In the study, Modal, Tencel, polyethylene teraphtalete, and cotton fibers represent micro, regenerated, synthetic, and natural fibers were used for the production of the 29.50 Tex yarns. Cross-sectional views of the yarns were acquired according to the hard sectioning method, and the packing densities of yarns were calculated with image processing tools. Yarn packing densities were calculated as the ratio of total fiber area within the yarn cross-section to yarn cross-section. Results showed that single ply ring-spun and siro-spun yarns are in a more circular shape and have greater packing densities values than two-ply yarns. Besides, yarns produced from cotton fibers have the least packing density values in each spinning technology. Similar packing density values were obtained for micro Modal, Tencel, and PET single-ply and siro-spun yarns. Packing density values were also compared with USTER diameter and density values and significant relations between those values were found.

Parametric modeling of 2.5D woven composites based on computer vision feature extraction

The aim of this paper is to develop a comprehensive modeling strategy for creating a realistic representative volume element (RVE) of 2.5D woven composites. The strategy consists of two main parts: the extraction of geometric feature parameters and the establishment of a parametric voxel-mesh full-cell model (VFM). Firstly, a neural network model is constructed to achieve an accurate segmentation of yarn cross-sections from X-ray computed tomography (XCT) images. Secondly, geometric feature parameters are then extracted from the segmentation results using image algorithms. Finally, a parametric modeling method is proposed to establish the VFM of the material. To evaluate the performance of the VFM, its structural sizes, overall fiber volume fraction (FVF), and stiffness prediction accuracy are assessed. The comparison results indicate that the VFM achieves a fine mesoscale characterization and a high stiffness prediction accuracy.

Kinematic modeling with Micro-CT slice auxiliary calibration for 2.5D woven SiO2f/SiO2 composites

An algorithm combining Micro-CT slice auxiliary calibration and kinematic modeling method is proposed to automatically generate yarns with irregular cross-sections and central paths for 2.5D woven SiO2f/SiO2 composites. The initial boundary conditions of the kinematic modelling simulation are calibrated by extracting the yarn positions from the corresponding Micro-CT slices. The simulation parameters with the real physical meanings are also determined in the kinematic modelling calculation. An explicit contact algorithm for truss elements in the kinematic modelling simulation with the calibration boundary conditions is employed to calculate nodal displacement. The virtual geometry of 2.5D woven SiO2f/SiO2 composites including detailed geometry information such as irregular yarn cross-section and yarn waviness or crimp can be reconstructed, which are in good agreement with the yarn geometry structures observed in Micro-CT scanning slices. The reconstructed geometry model can reflect the change of textile configurations during weaving and solidification process. The developed high-fidelity modelling method can also be used to reconstruct the geometry model of other textile composites with complex meso-structures.

Development of Three-Dimensional (3D) Biodegradable Polyglycolic Acid Fiber (PGA) Preforms for Scaffold Applications: Experimental Patterning and Fiber Volume Fraction-Porosity Modeling Study.

Three-dimensional (3D) biodegradable polyglycolic acid fiber (PGA) preforms were developed as temporary scaffolds for three-dimensional tissue regeneration applications. Three-dimensional biodegradable polyglycolic acid fiber (PGA) preforms including various degrees of interlaced structures called 3D plain, semi-interlaced, and orthogonal woven preforms were designed. Analytical relations and finite element model-based software (TexGen) on fiber volume fraction and porosity fraction were proposed to predict scaffolds' stiffness and strength properties considering micromechanics relations. It was revealed that yarn-to-yarn space, density, and angles of all 3D PGA fiber preforms were heterogeneous and demonstrated direction-dependent features (anisotropy). Total fiber volume fractions (Vfp) and porosity fraction (Vtpr) predicted by analytic and numerical modelling of all 3D scaffolds showed some deviations compared to the measured values. This was because yarn cross-sections in the scaffolds were changed from ideal circular yarn (fiber TOW) geometry to high-order ellipse (lenticular) due to inter-fiber pressure generated under a tensile-based macrostress environment during preform formation. Z-yarn modulus (Ez-yarn) and strength (σz-yarn) were probably critical values due to strong stiffness and strength in the through-the-thickness direction where hydrogel modulus and strengths were negligibly small. Morphology of the scaffold showed that PGA fiber sets in the preform were locally distorted, and they appeared as inconsistent and inhomogeneous continuous fiber forms. Additionally, various porosity shapes in the preform based on the virtual model featured complex shapes from nearly trapezoidal beams to partial or concave rectangular beams and ellipsoid rectangular cylinders. It was concluded that 3D polyglycolic acid fiber preforms could be a temporary supportive substrate for 3D tissue regeneration because cells in the scaffold's thickness can grow via through-the-thickness fiber (z-yarn), including various possible mechanobiology mechanisms.

Application of image processing technology on testing blending ratio and blending irregularity of blended yarns

The blending ratio and blending irregularity of the blended yarn determine its property and quality. In this article, the image processing method was introduced to accurately and conveniently measure the blending ratio and blending irregularity of blended yarn by using images of the blended yarn cross sections. The Euclidean distance peeling method was applied to segment the adhered fibers to make them individual. Then, the fibers were classified according to characteristic parameters of fiber cross section such as color, shape, and area. The experiments were implemented to verify the accuracy and applicability of the image processing method to test the irregularity of blended bundles, slivers, and yarns by different fibers including polyester, viscose, and wool. The results show that the fiber identification error rate of the image processing method for blended bundles, compared with the designed, is less than 2%; the blending irregularity difference rate between image processing method and the manual counting method is less than 5% for blended sliver by sliver blending; the difference rate of the blending ratio of polyester/viscose blended yarn between designed and measured by image processing method is less than 5%, while manual counting method is less than 10%. The findings mean that the image processing method proposed in this article can greatly save labor and time on identifying and counting fibers, and it is a more accurate, convenient, and reliable method to test blending irregularity.

Effect of Yarn Physical Properties on Fiber Migration and Packing Density of Cotton/Acrylic Blended Yarns

In the scope of the study, the effect of fiber blending ratio, yarn count and twist coefficient on fiber migration, packing density and diameter of the cotton/acrylic blended yarns were investigated. The yarn samples with 75-25%, %50-50%, 40-60% cotton-acrylic blending ratios were produced with three different yarn numbers; 20/1 Ne, 24/1 Ne, 30/1 Ne and three twist coefficients; 3.5 α, 4 α, 4.5 α. Thus, totally 27 yarn samples were obtained. The yarn cross-sectional samples were sliced with microtome. The image frames of yarn cross-sections were acquired via digital microscope. The yarn packing density was calculated by using image processing algorithm and the fiber migration was determined via cross-section images. The results were evaluated statistically.

Yarn modeling and winding process simulation based on 3D beam elements

In order to study the tension variation of cotton yarn in the winding process, a finite element model of yarn based on three-dimensional beam elements is proposed. As the size of yarn in the length direction is much larger than the cross-sectional size, this paper assumes that the yarn cross-section is circular and ignores the change of the cross-sectional area in the winding process. The winding process of yarn is simulated using Abaqus dynamic explicit, and the influence of the yarn fineness on the yarn tension during winding is analyzed. The results show that the average relative error between the simulation results and the experimental data is 14.09%, and the maximum relative error is 17.06%; therefore the model is reasonable. Compared with the solid element model of yarn, the yarn simulated by this model can save a lot of computing resources while taking into account the yarn stacking effect. The winding length that can be simulated in the same time is tens of times that of the solid element model, thus the winding simulation of nine-layer yarn on the bobbin is realized. The conclusion is that the inner yarn loop presents weak tension while the outer yarn loop has large tension.

FE modeling of woven fabric at the fiber bundle level under ballistic impact

In previous studies, ballistic impact on the fabric panel was usually simulated at the yarn level, which failed to capture ballistic responses of fibers. This study aims to employ a finite element model based on fiber bundle level to investigate the influence of fabric architecture on ballistic responses. The ballistic performance of fabrics with different architectures was investigated first through ballistic tests. The architecture parameters including aspect ratio of the yarn cross-section and yarn crimp ratio were found to be the dominant factors, which were further investigated through finite element modeling. Finite element results showed that finite element modeling at the fiber bundle level can lead to an increase of frictional energy dissipation during ballistic impact. For the yarn cross-section shape, reduction of the aspect ratio was beneficial on energy absorption due to better fracture synchrony of fibre bundles under impact. The crimp yarn path had a negative effect on stress wave propagation. When yarns were interlaced, the yarn cross-overs in fabric have further hindered the stress wave propagation. In comparison with the low crimp fabric, the fabric with the higher crimp ratio possesses a wider transverse deformation area under impact. Correspondingly, in the high crimp fabric more yarns were involved in the transverse deformation, which resulted in higher energy absorption. However, high stress concentration on the high crimp yarns can result in premature failure of fibers at the impact area. Such results contribute to a further understanding of ballistic responses from different hierarchies of fabric during ballistic impact.

Process-structure-performance modelling and progressive damage analysis of 3D rotary-four-directional rectangular braided composites under tensile load

The mechanical properties of braided composites are sensitive to the braiding process. However, the relations between process parameters, yarn structures and mechanical properties of three-dimensional (3D) rotary braided composites have not been investigated. In this study, we aim to establish a model capable of characterizing the yarn structures and mechanical properties of 3D rotary braided composites by treating braiding angles as primary variables. Carrier motions on the bedplate were traced by mathematical functions, where corresponding yarn spatial paths within a representative volume element (RVE) were explored. A parametric finite element model (FEM) of 3D rotary-four-directional (3DR4d) braided composites was established considering realistic yarn cross-sections. A progressive damage model was used to predict the mechanical performance of the composites. Experiments were conducted to verify the proposed model. The results show that the ideal yarn topology of the rotary braided composites is similar to the lattice structure. In addition, the longitudinal tensile modulus and strength of 3DR4d braided composites increase with the decreased braiding angles, while increasing with the increased fiber volume fractions. According to damage analysis, longitudinal tension and transverse shear are the dominant failure modes of 3DR4d composites with small and large braiding angles, respectively.

Computer Geometric Modeling Approach with Filament Assembly Model for 2 × 1 and 3 × 1 Twill Woven Fabric Structures

Abstract A new computer geometric modeling approach for 2 × 1 and 3 × 1 twill woven fabric structures is proposed. The precise geometrical description is presented by taking the skewness property into account. In the 2 × 1 and 3 × 1 twill weaves, the twill fabrics are formed of asymmetric floatings in which the length of floating sections was not equal on both surfaces and therefore the equilibrium condition was different from symmetric floatings. The proposed algorithm has three main parts: the first part describes the two-dimensional model of yarn cross-section for twill woven fabric structure, the second part consists of a modeling method for a three-dimensional model in warp/weft yarn, and the third part contains the CAD model. Examples of this approach are demonstrated and compared with a single line of yarn path model and the filament assemble model that excludes the skewness property. The model simulated in this study can improve the visual simulation of the real twill woven fabric and also this geometric model necessary as an input to many computational models for the prediction of the properties of the fabrics.