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|Title:||Study the permeability of multi-layer woven fabrics||Authors:||Liu, Yi||Keywords:||Hong Kong Polytechnic University -- Dissertations
Textured woven fabrics -- Permeability
|Issue Date:||2006||Publisher:||The Hong Kong Polytechnic University||Abstract:||The aim of this study is to explore the permeability of 3D multi-layer woven fabrics and the mechanism of void formation due to the permeability difference within it. The results provide theoretical support for designing and producing high-performance composite materials. Realizing the limitations of most existing models, which do not offer a realistic representation of the woven fabric architecture, the present developments introduce the notion of a micro/macro unit cell from a different perspective and are based on a more realistic representation of the three-dimensional fabric architecture which includes stitch, spacing and other fabric parameters. New models to study the effect of fabric microstructure and other properties of 3D multi-layer woven fabrics on permeability have been discussed. A permeability model based on fractal theory was established to predict the permeability of the preform fabricated with porous yarns. At the same time, another permeability model based on a unit cell of quadratic fibre packing was also proposed to predict the permeability of the 3D multi-layer woven fabrics fabricated with mono-filaments. It has been demonstrated that stitch structure plays an important role in the permeability of 3D multi-layer woven fabrics. The relationship between the fabric microstructure parameters and permeability has been established. The experimental validation of these two models was conducted over a series of stitch structures and the tendency predicted by the model agreed with the experimental data.
The mechanism of void formation in the multi-layer woven fabrics was also studied. The objective of current study is to carry out a theoretical analysis of in-plane impregnation in multi-layer woven fabrics (MWFs) to understand the mechanism of void formation. Unlike the previous work, where the void was formed in the plane of one layer of woven fabric, in this thesis void formation in a cross-section of MWFs was studied. In this thesis, two simplified unit cells for in-plane impregnation in multi-layer woven fabrics were suggested. A mathematical model was developed to describe the mechanism of void formation during the resin transfer moulding (RTM) processes. The flow fronts and void formation in these two cells were also numerically simulated using the control-volume method. The simulated results agree well with the results predicted by the mathematical models and verified by the experimental studies. The results show that, for a given fibre preform, the ratio of the weft axial permeability to the warp transverse permeability is responsible for the formation of void and the void size. A numerical simulation based on the control volume method was used to simulate the effect of stitch structure on equivalent permeability of the interbundle channels. The results show that the stitches would severely affect the permeability of the channels, even if the size of the stitches was very small. So this effect has to be considered when establishing the effective permeability model of multi-layer fabrics with stitches. The numerical simulation also demonstrates that the permeability varied greatly with the stitch changing in terms of the stitch size, off-centre position, slope, array, distribution density in the flow direction, and average Darcy velocity in the fibre bundles. Several 3D multi-layer woven fabrics were designed and six kinds of fabrics with different stitch structures were produced. These specimens were tested using in-plane permeability measurement based on the radial flow method. The predictions from the permeability models and the data obtained from the numerical simulation were well supported by the experimental results.
|Description:||xvii, 258 leaves : ill. ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P ITC 2006 Liu
|URI:||http://hdl.handle.net/10397/3563||Rights:||All rights reserved.|
|Appears in Collections:||Thesis|
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