Yarn Direction Research Articles

Damage and failure of triaxial braided composites under multi-axial stress states

Damage and failure of triaxial braided composites under multi-axial stress states was investigated. In order to introduce different multi-axial stress states in the material, uni-axial tensile tests were performed at different off-axis orientations. Three braid architectures, comprising braiding angles of 30°, 45° and 60° were each loaded parallel to their axial, transverse and braid yarn direction. Digital image correlation measurement techniques were used to quantify the effects of the textile architecture and its heterogeneity on the strain field, to identify and locate constituent failure mechanisms and to investigate damage initiation and development. In order to identify the driving physical mechanisms behind the material non-linearity, the evolution of the damage variable and the accumulated inelastic strain was quantified using incremental loading/unloading experiments. A high-speed camera was employed in order to study the dynamic nature of catastrophic failure. The triaxial braids within this study exhibited severe non-linearities in the mechanical response before final failure as a result of extensive matrix cracking. While we found the underlying textile architecture to slightly reduce the elastic properties compared to equivalent tape laminates, it functions as a natural crack arresting grid. As a result of this mechanism, braids under certain load conditions were capable of withstanding a higher strain to failure, even if a large portion of the specimen surface was saturated with matrix cracks. The accompanying mechanical behaviour can be desirable in the design of crash absorbing or pseudo-ductile materials. An additional failure mode intrinsic to the textile architecture was encountered for loading in the heavily undulated braid yarn direction. Due to yarn straightening and out-of-plane movements, braided composites were found to fail as a result of large scale delaminations accompanied by progressive fibre bundle pull-out.

Modeling PVC-coated polyester as a hypoelastic non-linear orthotropic material

A hypoelastic non-linear orthotropic material model was characterized for two different PVC-coated polyesters from uniaxial tests in the warp, fill, and 45° bias yarn directions. Ultimately the non-linear orthotropic material model fails to capture the full behavior of PVC-coated polyester. Thus the determination of material parameters depends upon which experimental response is the most important for the model to capture. Two methods are presented for determining different parameters for the non-linear orthotropic material, such that each method captures a particular aspect of the material’s response better than the other method. The first approach derives the stiffness moduli as a function of strain from the experimental stress–strain response of the uniaxial tests. The second approach utilizes an inverse analysis, powered by an optimization routine, to find the best material parameters such that the experimental load–displacement response is matched in the finite element (FE) model. Additional the Poisson’s effect was investigated, and the transverse uniaxial behavior is presented.

Mechanical analysis of 3D braided and woven composites using fiber-based continuum analysis

A numerical method was developed to reflect the microstructural changes of 3D textile composites and to predict their mechanical behavior based on continuum mechanics framework. The first step of the new method is to define the yarn orientation at every point of 3D textile composites and to update the yarn orientation using the deformation gradient. 3D textile composites are assumed as a combination of several uni-directional layers, each of which represents continuous distribution of fibers in the yarn direction. The tangent stiffness of each layer is then computed considering the yarn undulation, followed by calculation of the stress increment. Damage initiation is then evaluated using Puck’s criterion and its propagation is implemented using modified ply discount method. The proposed numerical method was incorporated into commercial finite element software through a user material subroutine. The mechanical behavior of 3D braided and 3D woven composites was then predicted and compared with experimental to demonstrate the validity of the developed method.

Effect of equi-biaxially fabric prestressing on the tensile performance of woven E-glass/polyester reinforced composites

The tensile properties of prestressed fabric-reinforced composites have been investigated. A method of applying an equi-biaxially fabric prestressing prior to and during the curing process of a plain-weave fabric composite was performed. A novel fibre prestressing equipment was built to apply and measure the tension load in the principal yarn directions of a fabric. The equi-biaxial fabric prestressing level, ranged from zero to 100 MPa, was used. Tensile tests were performed for the batches with different fabric prestressing levels to estimate the optimum level that gives the maximum tensile performance. The samples were also tested at different orientation angles, precisely from warp to bias direction. Prestressing the fabric enhanced the tensile performance such as elastic modulus and critical stress to first fracture of the composite by 10–20%. Most tensile properties, for instance tensile modulus and critical stress, reached their ultimate values at 50 MPa of prestressing level; however, the tensile-limited toughness was maximum at a level of fabric prestressing of ∼75 MPa.

Characterization of the Mechanical and Fatigue Behavior of Braided Composites Made of Twisted Yarns

In this study an experimental investigation was undertaken to characterize the influence of twisted yarns on the mechanical and fatigue behavior of 2D braided composites with a braiding angle of ±45°. Rectangular specimen made of untwisted and twisted carbon yarns are tested in the braiding (±45° fiber orientation) and in the yarn direction (0/90° fiber orientation). Experimental results will include modulus and strength values based on tensile and compression tests for both test directions. In addition, the effect of fiber twisting on S/N-curves are discussed.

Research on mechanical properties of the Siro-spinning triangle using the Finite Element Method

Siro-spinning (two-strand yarn spinning) is a new kind of modified ring spinning method, which is achieved by feeding two rovings into the apron zone at a predetermined separation simultaneously. There are three spinning triangles, including two primary spinning triangles and one final spinning triangle, in Siro-spinning. Therefore, in this paper, the quantitative relationships between the mechanical performance of a Siro-spinning triangle and the spinning parameters are investigated by using the Finite Element Method. The finite element model of the Siro-spinning triangle is constructed under the assumption in which the constituent fibers are considered as three-dimensional elastic beam elements with tensile, compressive, torsion, and bending capabilities. Three different cases where the ends of all fibers, the initial strain of all fibers, and the angle between any two adjacent fibers gripped in the front roller nip distribute evenly are discussed. Meanwhile, in each case, three different cases where the initial strains of the shortest boundary fiber, the central fiber, and the virtual fiber on the direction of yarn spinning tension are set as zero are discussed respectively. Then, taking the spinning triangle in Ne40 (14.6 tex) cotton Sirospun yarn as an example, the fiber tension distribution and fiber torsion distribution in the corresponding Siro-spinning triangle with and without fiber buckling are numerical simulated. It is shown that the fiber tension distributions are influenced by the setting of the fiber initial strain, while the magnitudes of fiber tension are not affected. Finally, Ne40 cotton ring yarns were spun on an EJM128K ring spinning machine, and the properties of spun yarns were evaluated and analyzed according to the simulation results.

Prediction of elastic properties for woven z-pinned composites

Delamination occurs easily due to impact loads caused by the weakness of out-of-plane properties in composite materials. In order to overcome this problem of suppressing delamination, which is a critical weakness for composite materials, z-pinned composite material with reinforced out-of-plane elastic properties was developed by inserting z-pins into out-of-plane directions. In order to overcome the stability within the mutually orthogonal yarn direction of z-pinned composite material, a woven z-pinned composite was developed. This paper examines the effects of z-pin reinforcement on the elastic properties of composite materials as well as the changes in elastic properties used for the diameter of the z-pin, the length of the resin rich zone, and the length of yarn thickness by incorporating the graded fiber waviness that is created by the z-pin and graded warp and fill. As a result, we observed an increase in the out-of-plane properties of the woven z-pinned composite. Positive correlations were observed between the numerical model and experimental results.

Localized Detection of Damage in Laminated Composite Materials Using Carbon Nanotube Yarn Sensors

Carbon nanotube yarns are lightweight, stiff, strong, ductile and electrically conductivefiber-like materials that exhibit a piezoresistive response. This piezoresistive characteristicof the carbon nanotube yarns is being tapped to measure strain in polymeric andlaminated composite materials through resistance measurements without adding muchweight or altering the integrity of the host material. Furthermore, the same principle isbeing used to detect damage and delamination in laminated composite materials. Thispaper includes the experimental results of a study about damage detection in laminatedpolymeric composite materials using carbon nanotube yarn sensors. A combinationof sensor configurations including yarns stitched through the thickness direction of thecomposite laminate and yarns placed straight cross wide to the laminate are used todetect the presence of damage as well as its extent and propagation pattern. As thelaminated composite is mechanically loaded, the yarn sensors capture instantaneouslydelamination as demonstrated by their resistance response. Crucially, the yarn sensorsare sensitive enough to provide a significant resistance increase output that serves asan indication of an impending delamination. Minor damage such as porosity or otherfabrication details are also captured as evidenced by a small increase in the resistanceof the yarn sensor. The experimental results also show the ability of a combination of differentyarn sensors to detect the exact location and extent of the delamination throughoutthe entire loading process. Damage detection using carbon nanotube yarns mayoffer a highly adaptive, practical, and sensitive structural health monitoring method.

Geometrical modelling of 3D woven reinforcements for polymer composites: Prediction of fabric permeability and composite mechanical properties

For a 3D orthogonal carbon fibre weave, geometrical parameters characterising the unit cell were quantified using micro-Computed Tomography and image analysis. Novel procedures for generation of unit cell models, reflecting systematic local variations in yarn paths and yarn cross-sections, and discretisation into voxels for numerical analysis were implemented in TexGen. Resin flow during reinforcement impregnation was simulated using Computational Fluid Dynamics to predict the in-plane permeability. With increasing degree of local refinement of the geometrical models, agreement of the predicted permeabilities with experimental data improved significantly. A significant effect of the binder configuration at the fabric surfaces on the permeability was observed. In-plane tensile properties of composites predicted using mechanical finite element analysis showed good quantitative agreement with experimental results. Accurate modelling of the fabric surface layers predicted a reduction of the composite strength, particularly in the direction of yarns with crimp caused by compression at binder cross-over points.

Experimental and numerical analyses of the mechanical behaviors of three-dimensional orthogonal woven composites under compressive loadings with different strain rates

Quasi-static and high strain rate compressive behaviors of basalt/vinyl ester 3D orthogonal woven composites along three perpendicular yarn directions were investigated experimentally and numerically. An elastic–plastic numerical model based on the 3D fabric architecture of the 3D orthogonal woven composites was developed to analyze the compressive deformation and failure mode under different strain rate loading conditions. The stress–strain curves obtained from experimental along three directions were used to validate the finite element model. The agreement between the experimental and finite element model results proves the validity of the finite element model. From the experimental results, the strain rate sensitive and anisotropy of the compressive behaviors was found. The finite element results were employed to analyze the locations of stress propagation, the 3D stress state, and the progressive failure behavior. It was also found that this model has a similar failure shape of “broom” at one end of the composite along both of weft and warp compressive directions, while an inclined shear band was formed in through-thickness compression. This result indicates that Z-yarn contributed significantly to the in-plane responses. Additionally, the absorbed energies that induce the complete damage of the composite coupons at various strain rates were also calculated and discussed.

Analysis of the Blank Holder Force Effect on the Preforming Process Using a Simple Discrete Approach

Simulation of the dry reinforcement preforming, first step of the Resin Transfer Moulding process, become necessary to determine the feasibility of the forming process, compute the fiber directions in the final composite component, and optimize process parameters during this step. Contrary to geometrical approaches, based on fishnet algorithms, finite element methods can take into account the actual physical parameters, the real boundary conditions and the mechanical behavior of the textile reinforcement. The fabric can be modeled either as continuum media with specific material behavior [5, 6], or using discrete structural elements to describe the textile structure at the mesoscopic scale. A semi-discrete approach, which is a compromise between the above continuous and discrete approaches, is also used for simulation. A discrete approach for the simulation of the preforming of dry woven reinforcement has been proposed and presented in a previous paper. This modelling is based on a “unit cell” formulated with elastic isotropic shells coupled to axial connectors. The connectors, which replace bars or beams largely studied in other discrete approaches, reinforce the structure in the yarn directions and naturally capture the specific anisotropic behavior of fabric. Shell elements are used to take into account the in-plane shear stiffness and to manage contact phenomena with the punch and die. The linear characteristic of the connectors, has been extended to a non linear behaviour in the present paper to better account for fabric undulation. Using this numerical model, we propose, in this work to study the effect of process parameters on the woven fabric deformation during the performing step. The emphasis will be placed on the analysis of the influence of the blank holder pressure on the shear angle distribution.

Effect of Weaving Direction of Conductive Yarns on Electromagnetic Performance of 3D Integrated Microstrip Antenna

A three-dimensionally integrated microstrip antenna (3DIMA) is a microstrip antenna woven into the three-dimensional woven composite for load bearing while functioning as an antenna. In this study, the effect of weaving direction of conductive yarns on electromagnetic performance of 3DIMAs are investigated by designing, simulating and experimental testing of two microstrip antennas with different weaving directions of conductive yarns: one has the conductive yarns along the antenna feeding direction (3DIMA-Exp1) and the other has the conductive yarns perpendicular the antenna feeding direction (3DIMA-Exp2). The measured voltage standing wave ratio (VSWR) of 3DIMA-Exp1 was 1.4 at the resonant frequencies of 1.39 GHz; while that of 3DIMA-Exp2 was 1.2 at the resonant frequencies of 1.35 GHz. In addition, the measured radiation pattern of the 3DIMA-Exp1 has smaller back lobe and higher gain value than those of the 3DIMA-Exp2. This result indicates that the waving direction of conductive yarns may have a significant impact on electromagnetic performance of textile structural antennas.

A Simple Discrete Method for the Simulation of the Preforming of Woven Fabric Reinforcement

In this paper, a discrete approach for the simulation of the preforming of dry woven reinforcement is proposed. A “unit cell” is built using elastic isotropic shells and axial connectors instead of bars and beams used in previous studies. Shell elements are used to take into account the in-plane shear stiffness and to manage contact phenomenon with the punch and die. Connectors reinforce the structure in the yarn directions and naturally capture the specific behavior of the fabric. To identify the material parameters, uniaxial tensile tests and bias tests have been employed. A numerical algorithm, coupling Matlab and Abaqus/Explicit, is used to determine the shear parameters by an inverse method. The model has been implemented in Abaqus to simulate hemispherical stamping. Experimental results are compared to numerical simulations, good agreement between both results is shown.

Simulating the Manufacturing Process and Subsequent Structural Stiffness of Composite Wind Turbine Blades with and without Defects

Traditional ply-based and zone-based models are limited in their ability to account for the fiber directions resulting from the forming of fabric-reinforced composite wind turbine blades. Compounding the problem is the presence of defects such as resin-rich pockets of the polymer matrix due to out-of-plane and in-plane waves resulting from the manufacturing process. As a result, blades are typically overdesigned, unnecessarily increasing weight and material costs. In the current research, a methodology is presented for simulating the manufacturing process for fabric-reinforced composite wind turbine blades using ABAQUS/Explicit. The methodology captures the evolution of the yarn directions during the forming process thereby allowing for a map of the fiber orientations throughout the blade. A hybrid approach using conventional beam and shell elements is used to model the various fabric layers. Using experimental shear, tensile, bending, and friction data to characterize the mechanical behavior of the fabric layers, the model captures in-plane yarn waviness and changes in the in-plane yarn orientations as they conform to the shape of the mold, as well as out-of-plane wave defects as a result of the manufacturing process. Subsequently, after the fabric layers have been laid into the mold and the final yarn orientations are known, the structural stiffness of the blade resulting from the resin-infused fabrics can be calculated. The methodology can thereby link the resulting bending and torsional stiffnesses of the blade back to the manufacturing process. This paper discusses the methodology for determining the material properties of the beam and shell elements in their final orientations in the cured composite to predict the structural stiffness of a wind turbine blade.

Cad Software Based Design of Yarn Guide Profile

The traversing mechanism on a winding machine causes the yarn guide and hence the yarn to reciprocate. This work is an attempt to eliminate the too and fro motion of the yarn guide wherein the guide profile ensures proper transfer of yarn with the desired pattern and pitch. The change in yarn direction after completing one axial traverse poses the most challenging aspect in designing an efficient guide profile. With idealizing assumption of the yarn behaving as a thin wire under the taut condition between three support points at the top ring, profile point on the guide and the bobbin, the ideal profile for consistent guidance of the yarn has been developed.

Electromagnetic shielding characteristics of woven fabrics made of hybrid yarns containing metal wire

In this study, electromagnetic shielding characteristics of woven fabrics made of hybrid yarns are investigated. For this purpose, initially the hybrid yarns containing stainless steel wire are produced with hollow spindle covering technique, and then eight different fabric samples are produced using these hybrid yarns. Electromagnetic shielding values of fabric samples are determined by a test set up based on enclosure measurement technique. Measurements are made in the frequency range of 30 MHz-9.93 GHz. Test results show that woven fabric samples investigated in this study have 25–65 dB electromagnetic shielding effectiveness for incident frequency. It was also shown that the direction, density and settlement type of conductive hybrid yarn in fabric structure are important parameters affecting electromagnetic shielding characteristics of woven fabrics.

Study on the Composition and Explicit/implicit Effect of Woven Texture

The article discusses the impact of composition elements of fabric on explicit/implicit effect of woven texture, which aims to form basic ideas of designing fabric appearance effect. Based on analyzing the composition of fabric texture, the author highlights the effect of fabric composition elements, such as materials, weave and density, on the clarity of fabric texture, The result shows that the weave grain will be clearer when the twists of warp and weft yarns are in the same direction. The weave grain will be less clarity as the increase of fabric voidage. The clarity of Jacquard fabric depends on the basic weave and yarn direction.

Effect of Frictions on the Ballistic Performance of a 3D Warp Interlock Fabric: Numerical Analysis

3D interlock woven fabrics are promising materials to replace the 2D structures in the field of ballistic protection. The structural complexity of this material caused many difficulties in numerical modeling. This paper presents a new tool that permits to generate a geometry model of any woven fabric, then, mesh this model in shell or solid elements, and apply the mechanical properties of yarns to them. The tool shows many advantages over existing software. It is very handy in use with an organization of the functions in menu and using a graphic interface. It can describe correctly the geometry of all textile woven fabrics. With this tool, the orientation of the local axes of finite elements following the yarn direction facilitates defining the yarn mechanical properties in a numerical model. This tool can be largely applied because it is compatible with popular finite element codes such as Abaqus, Ansys, Radioss etc. Thanks to this tool, a finite element model was carried out to describe a ballistic impact on a 3D warp interlock Kevlar KM2® fabric. This work focuses on studying the effect of friction onto the ballistic impact behavior of this textile interlock structure. Results showed that the friction among yarns affects considerably on the impact behavior of this fabric. The effect of the friction between projectile and yarn is less important. The friction plays an important role in keeping the fabric structural stability during the impact event. This phenomenon explained why the projectile is easier to penetrate this 3D warp interlock fabric in the no-friction case. This result also indicates that the ballistic performance of the interlock woven fabrics can be improved by using fibers with great friction coefficients.

Advantages of the Meso/Macro Approach for the Simulation of Fibre Composite Reinforcements

This paper presents a new discrete modelling for the dry woven composite reinforcements forming in LCM (Liquid Composite Moulding) processes. Two existing approaches to model woven composite reinforcements at the macroscopic and mesoscopic scale are reminded and our modelling at the mesoscopic scale which can be applied to large fabric pieces is presented. The mechanical behaviour of each compound in such a model is simpler than for continuous models and difficult aspects such as yarn's direction updating are naturally built in as in the mesoscopic approach. The compensation lies in the large amount of components with complex contacts between them. Interests of this approach such as the prediction of the apparition of wrinkles and “unweaving” phenomena are also detailed and illustrated by the simulation of a picture frame test and of a deep drawing forming.

Mesoscopic Strains Maps in Woven Composite Laminas During Off-axis Tension

The mechanics of woven carbon-fiber reinforced plastic (CFRP) composites is influenced by the complex architecture of the reinforcement phase. Computational (i.e. finite element based) approaches have been used increasingly to model not only the global laminate stiffness, but also damage evolution and laminate strength. The modeling combines the identification of the architectural unit cell (UC), the selection of suitable constitutive models of the different phases, the creation of a fine discretization of the UC in finite elements, the application of an incremental solution procedure that solves iteratively for the stresses and strains in the UC, [1].The experimental validation of computational models is carried out mainly at the macroscopical level, i.e. simulation of the macroscopic stress-strain curve. Damage, however, is a localized, straindependent phenomenon and therefore only accurate strain distribution within the UC (at the mesolevel) can identify critical conditions in terms of damage location, extension and evolution.The validation of computational damage procedures is a key task and full-field optical strain analysis methods appear the ideal instrument. However, only limited examples of direct finte element method (FEM) vs experimental strain correlation are found because of the limited sensitivity and spatial resolution of some techniques and the complexity and applicative difficulty of others.The aim of the present paper is to present the application of the digital image correlation (DIC) technique, [2], to the full-field strain analysis at the mesoscopic level (i.e. within the UC) of a woven CFRP lamina when the direction of loading forms an angle to the material direction.The material under consideration is a woven carbon fiber reinforced epoxy composite. Orthogonal yarns, each made of of several thousand fibers, are woven according the twill-weave architecture is shown in Fig. 1a. Single-ply laminas were manufactured and tested to eliminate the random 3D influence of multiple-ply laminates and to favor computational model validation.Specimens with different loading directions with respect to the material principal directions were prepared and tested in a servo-hydraulic testing machine. Specimen surface preparation consisted in a speckle pattern generation to allow the application of the DIC tecnique. During the tensile experiment, the speckle pattern is recorded (frame rate of 0.1 picture/second) using a CCD camera equipped with a microscopic lens and adjustable light sources. In-house DIC software was used for in-plane displacement and strain determination and mapping.For brevity only the case of loading in the tow yarn direction is considered here. Fig. 1b shows a tipical strain map obtained with the DIC technique at an applied macroscopic strain of 0.9%. The strains are small but the DIC dechnique is sensitive enough and suitable filtering reduce the noise level of the strain maps. Strong local strain gradients are determined and referred to the yarn architecture in Fig. 1c. The DIC measurements were validated by averaging the strain over the field of view and comparing it with the macroscopic strain given by a high-sensitivity MTS extensometer.The mesoscopic srain data obtained with DIC are used to assess and validate parallel material model development by direct FEM vs experimental strain correlation. Fig. 2a shows the FEM model of the unit cell for the twill-weave architecture with a detail of the yarn geometry and finite element discretization. Suitable boundary conditions are applied to the UC model contours before the analysis, [1]. Fig. 2b shows and example of the comparison of the local longitudinal FEM/DIC strain distribution along a transverse line of Fig. 1c. The comparison shows the excellent correlation achieved both in terms of gradients and absolute strain values, [3].