Stochastic modelling of textile structures for resin flow analysis

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simulation of transient flow through a randomised filament arrangement was made. It was hypothesised that steady-state flow results may be used for the prediction of transient flow

Influence of the micro-structure on saturated transverse flow in fibre arrays

This study analyses the influence of the random filament arrangement in fibre bundles on the resin flow behaviour. Transverse steady-state resin flow which occurs behind a liquid resin flow front was simulated numerically through statistically equivalent micro-structures at high fibre volume fractions, Vf >0.6, as observed in fibre bundles. The need of applying a minimum gap distance between neighbouring filaments was overcome by automated local mesh refinement. The derived permeability values showed significant scatter. Convergence of these values was determined at a ratio of flow length to filament radius greater than 20 for all three analysed fibre volume fractions. Mean permeabilities were between 6 and 10 times lower than those predicted for a hexagonal fibre array. A statistical model is proposed which is able to predict the scatter of observed permeabilities based on simple micro-structural descriptors

Modelling framework for optimum multiaxial 3D woven textile composites

The application of 3D weaves has advantages over conventional uni-directional or 2D woven lay-ups. There is potential to produce near net-shaped preforms and to increase damage resistance due to the presence of through thickness reinforcement. Conventional 3D weaves typically consist of orthogonal yarns interwoven with through thickness binder yarns. This paper describes a feasibility study to find optimum architectures for 3D woven fabrics where some of the normal manufacturing constraints are relaxed. This will provide the basis for development of novel manufacturing methods based on optimum textile architectures. A framework has been developed for the automatic generation and analysis of 3D textile geometries, utilising the open-source pre-processor TexGen. A genetic algorithm is used to select an optimum geometry by evaluating results from finite element simulations using the commercial solver Abaqus. This paper highlights the flexibility of TexGen software to create complex 3D models by means of its Python scripting application programming interface (API). A standard layer-to-layer geometry is used as a starting point to which off-axis yarn rotations, in-plane shift of entire layers and adjustments to binder yarns can be applied. Geometric variables are selected to represent the textile architecture enabling the automation of unit cell creation and finite element analysis. A Genetic Algorithm is used to determine the optimum through thickness binder path, the number and the width of the binders, and yarn angles using a weighted objective function of the material elastic properties. The case studies show that the algorithm is efficient to converge to the optimum fibre architecture

Quantification of mesoscale variability and geometrical reconstruction of a textile

Automated image analysis of textile surfaces allowed determination and quantification of intrinsic yarn path variabilities in a 2/2 twill weave during the lay-up process. The yarn paths were described in terms of waves and it was found that the frequencies are similar in warp and weft directions and hardly affected by introduced yarn path deformations. The most significant source of fabric variability was introduced during handling before cutting. These resulting systematic deformations will need to be considered when designing or analysing a composite component. An automated method for three dimensional reconstruction of the analysed lay-up was implemented in TexGen which will allow virtual testing of components in the future

Stochastic modelling of textile structures for resin flow analysis

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simulation of transient flow through a randomised filament arrangement was made. It was hypothesised that steady-state flow results may be used for the prediction of transient flow.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Modelling framework for optimum multiaxial 3D woven textile composites

The application of 3D weaves has advantages over conventional uni-directional or 2D woven lay-ups. There is potential to produce near net-shaped preforms and to increase damage resistance due to the presence of through thickness reinforcement. Conventional 3D weaves typically consist of orthogonal yarns interwoven with through thickness binder yarns. This paper describes a feasibility study to find optimum architectures for 3D woven fabrics where some of the normal manufacturing constraints are relaxed. This will provide the basis for development of novel manufacturing methods based on optimum textile architectures. A framework has been developed for the automatic generation and analysis of 3D textile geometries, utilising the open-source pre-processor TexGen. A genetic algorithm is used to select an optimum geometry by evaluating results from finite element simulations using the commercial solver Abaqus. This paper highlights the flexibility of TexGen software to create complex 3D models by means of its Python scripting application programming interface (API). A standard layer-to-layer geometry is used as a starting point to which off-axis yarn rotations, in-plane shift of entire layers and adjustments to binder yarns can be applied. Geometric variables are selected to represent the textile architecture enabling the automation of unit cell creation and finite element analysis. A Genetic Algorithm is used to determine the optimum through thickness binder path, the number and the width of the binders, and yarn angles using a weighted objective function of the material elastic properties. The case studies show that the algorithm is efficient to converge to the optimum fibre architecture

Experimental determination of the permeability of textiles: a benchmark exercise

In this international permeability benchmark exercise, in-plane permeability data for two reinforcement fabrics, obtained using a total of 16 different experimental procedures, were compared. Although, for each procedure, the results appear consistent, different procedures result in a scatter of up to one order of magnitude in principal permeability values for each fabric at any given fibre volume fraction. The ratio of the principal permeability values varies by factors of up to 2. While experimental uncertainties and variability of the specimens affect the scatter in results for any single series of experiments, it is suspected that the main source of scatter in results from different procedures is related to human factors. Aiming at standardisation of measurement methods and interchangeability of results, "good practice" guidelines will be formulated in order to eliminate sources of scatter. (C) 2011 Elsevier Ltd. All rights reserved.status: publishe