Fibrous Tows Research Articles

Modeling of fibrous tow transmission considering residual strain and friction

This study established a mechanical model based on the mechanical properties of fibrous tows and their force of interaction with spools. The proposed model not only describes the hysteresis, nonlinear elastic, and viscoelastic stress components, but also analyzes the effect of residual strain on aramid fiber mechanical properties. Moreover, the effect of the interaction force between the fiber and spool on the transmission accuracy should be considered. Contrary to the conventional view, hysteresis is caused not only by internal sliding among molecules and molecular chains but also by friction between the fibers and spools. To assess this effect, several monotonous and cyclic tensile tests were conducted, with the results showing that the maximum relative error of the mechanical model did not exceed 5%. The proposed mechanical model can help designers determine effective carrying ranges and predict the fiber mechanical behavior, thereby laying a foundation for achieving nonlinear control of the fibrous tow transferring load.

Meso-scale compaction simulation of multi-layer 2D textile reinforcements: A Kirchhoff-based large-strain non-linear elastic constitutive tow model

This paper presents a non-linear, large strain constitutive approach to modelling the mechanics of fibrous tows. The isotropic and linear St. Venant hyperelastic model was modified to extend its applicability to a transversely isotropic continuum. From this model, a set of large-strain material parameters which resemble the linear-elastic moduli was derived. The non-linear constitutive response of fibrous tows was accounted for through a modelling scheme that incorporates the instantaneous microstructural arrangement of the tows. Tow samples were isolated from the studied textile roll and subjected to a compression study utilising a custom-made tow compression rig, from which a set of material functions that fully defined the constitutive model were generated. The developed model was then implemented as a material subroutine and utilised in a mesoscopic compaction simulation of a multi-layer 2D woven reinforcement. It was found that the constitutive model performed very well in predicting the shape changes and stresses in deforming tows.

Particle simulation of dual-scale flow in resin transfer molding for process analysis

Modeling the inhomogeneous microstructures of fibrous tows is important for analyzing the process of resin transfer molding because dual-scale pores in a preform can lead to void formation. This study focused on the development of a microscopic flow analysis method to predict the impregnation of fiber bundles. The moving particle semi-implicit method was adopted to model the microstructure of a fiber bundle explicitly and inter-particle potential force was introduced into the numerical model to take account for the capillary effect. The predicted process of impregnation and void formation agreed with empirical observations. The developed approach was applied to predict the relationship between the modified capillary number and void content to identify the optimal molding conditions to reduce microvoids. The obtained relationship reproduced the trends of a reported experiment, which indicates that the proposed approach will provide information about optimal conditions for minimizing void content.

Modelling process induced deformations in 0/90 non-crimp fabrics at the meso-scale

The manufacture of non-crimp fabric composites typically requires the forming and consolidation of the reinforcement material. During this process the material is subjected to complex loading where the coupling of tensile, bending, shear and compressive forces result in deformations to the internal architecture of the textile. To determine the extent of these deformations a numerical modelling method has been developed to capture the kinematic behaviour of non-crimp fabric textiles. This method focuses on capturing the interactions between the fibrous tows and the stitch yarns which bind the tows together. Through modelling at a level of detail in which the meso-scale interactions are explicitly present, the macro-scale behaviour of the material proceeds naturally within the model, negating any requirement for detailed characterisation of the physical material. This also enables a detailed description of the internal architecture of the deformed fabric to be extracted for analysis or further modelling. The present study explores the method's ability to capture both local and global deformations which occur in non-crimp fabrics, specifically to capture the onset of deformations that appear due to tow-stitch interactions and the forming and compaction of multiple layers. Comparison with experimental results show good agreement for both meso-scale deformations, resulting from multi-layer compaction, and global in-plane shear deformations induced through forming over complex tooling.

Using micro-CT to quantitatively validate the textile compaction simulation

The results of any dry textile compaction simulation have to be validated. Micro-CT is a perfect tool to facilitate such a task. By performing an equivalent dry textile compaction experiment inside a micro-CT, the actual deformation and placement of fibrous tows can be captured within a sample as it deforms. The resulting micro-CT images can readily be used to qualitatively validate a compaction model. This work presents a set of methodologies to facilitate a straight forward quantitative comparison between a micro-CT sample and an equivalent compaction model. The images from the micro-CT and the compaction models are subjected to various image processing techniques that are implemented in MATLAB. The program is designed to allow a user to process the images in a consistent and semi-automated manner while minimising the manual labour time. Various cross-sectional parameters of the tows at each image slice are computed automatically using an algorithm that can handle any arbitrarily shaped cross section. By presenting the computed data as a series of Excel files and 3D plots, this work concludes that micro-CT can be used to conveniently quantitatively validate the result of compaction models.

Image-based modeling of moisture-induced swelling and stress in 2D textile composite materials using a global-local approach

The present paper focuses on the employment of a global-local approach for the simulation of moisture-induced swelling and stress in a 2D textile carbon fiber/epoxy matrix composite material. The approach is based on the development of a robust image-based finite element model built starting from X-ray microtomography scans of a repetitive unit cell of the textile material: simulations aim at investigating both the global (sample scale) level and the local micromechanical (interfaces between matrix and fibrous tows, matrix inside a tow) level behaviour. Three models at the different cited scales are first built (ply level model, tow level and fiber level model): then a non-concurrent (node-based) approach is used for coupling the models at different scales. The results of numerical simulation of moisture-induced swelling and stress are discussed, with emphasis on the identification of the most critical zones at which maximal stress values are calculated, at different scales.

Frictional behavior of carbon fiber tows: a contact mechanics model of tow–tow friction

Composite-forming processes involve mechanical interactions at the ply, tow, and filament level. The deformations that occur during forming processes are governed by friction between the contacting tows on the mesoscopic level and consequently between filaments on the microscopic level. A thorough understanding of the frictional properties at the level of individual filaments is essential to understand and to predict the macroscopic deformations of a textile reinforcement during forming. This work presents a contact mechanics modeling approach to provide a theoretical background of the frictional behavior of dry fibrous tows in contact with each other. The predicted frictional behavior is in qualitative and quantitative agreement with experimentally observed frictional forces of carbon fiber tows in sliding contact. The relative orientation of the contacting tows is of great importance for the developed frictional forces in the contact.

Frictional behaviour of high performance fibrous tows: A contact mechanics model of tow–metal friction

Composites forming processes involve mechanical interactions on the ply, tow, and filament level. 0The deformations that occur during forming processes are governed by friction between tows and tooling material on the mesoscopic level and consequently between filaments and a counterface on the microscopic level. A thorough understanding of the frictional properties on the level of individual filaments is important to understand and predict the macroscopic deformations of a fabric during forming. The contact mechanics based friction model in this work confirms an experimentally observed decrease of frictional forces with an increasing roughness of the counterface. The developed model provides a qualitative understanding of the frictional behaviour of filaments on a cylindrical metal counterface.

Frictional behaviour of high performance fibrous tows: Friction experiments

Tow friction is an important mechanism in the production and processing of high performance fibrous tows. The frictional behaviour of these tows is anisotropic due to the texture of the filaments as well as the tows. This work describes capstan experiments that were performed to measure the frictional behaviour of aramid, carbon and E-glass tows, both in tow-metal and tow–tow contact. The effects of anisotropy and other processing-related parameters on the frictional behaviour of the tows are discussed. The surface topography of the counterface plays a dominant role in tow-metal friction. For tow–tow contact, the relative orientation of the tows dominates the frictional behaviour.

Tow Mechanics: A Contact Mechanics Approach of Friction in Fibrous Tows during Forming

Composites forming processes involve mechanical interactions on the ply, tow, and filament level. The deformations that occur during forming processes are governed by friction between tows and tooling material on the mesoscopic level and consequently between filaments within the tows on the microscopic level. A thorough understanding of the frictional properties of individual filaments is essential to understand and to predict the macroscopic deformations of a fabric during forming. This paper provides a global description of the experimental and modelling approaches to explain the contact friction between fibrous tows and metal tooling material, focusing on contact mechanics at the tow and filament scale.

Friction measurements on carbon fibre tows

Friction plays an important role in the production of fibre reinforced composite products. The fibrous tows deform during the forming phase. Friction is regarded as a dominant phenomenon in tow deformation mechanisms. The coefficient of friction is a material-interface characteristic which gives a relation between applied deformation loads and frictional forces. A capstan experiment has been performed with carbon fibre tows on a steel cylinder. This work aims to clarify friction related mechanisms and identify dominant parameters. The applicability of the capstan experiment is investigated with respect to the frictional behaviour of fibrous tows.

A methodology for Cartesian braiding of three-dimensional shapes and special structures

Cartesian three-dimensional braiding as a method of preforming has been investigated. The design of complex and unusual 3-D braids was studied in three parts. These are the grouping of yarns, the fabrication of braids with a complex cross-section, and braids with surrogate material (replacing fibrous tows) added or removed. The grouping of yarns to potentially form hybrid composites was studied via an iterative simulation of the braiding process. Through further analysis of the braid cycles which produce specific yarn grouping, it was found that isolation/insertion rows and columns may be used to quarantine yarns within desired areas of preform cross-section and improve interlacing of the braided structure. In this study, the design of braided composite cross-sectional shape is accomplished through adaptation of the Universal Method. A computer algorithm has been developed which allows the desired cross-sectional shape to be specified and a braid plan for its fabrication automatically determined. A number of 3-D braids, the result of variations or extensions to Cartesian braiding, are also presented. These have been classified as those with axial and transverse yarn insertion, structures with voids, and fillers and fasteners. Braiding equipment has been developed to braid the designed structures. The machines have been used to fabricate four-step braids with transverse, fastener, and filler insertion, special hybrid structures from multiple row and column displacement and multi-step cycles, and uniquely shaped structures with constant and varying cross-sections along their lengths.