Permeability modelling of Non-Crimp Fabrics (NCFs)

In this report, we will perform a qualitative study on the in-plane permeability modelling of Non-Crimp Fabrics (NCFs). For this, a network flow model will be created to explain flow through inter bundle channels (meso level). These inter bundle channels are often called Stitch Yarn induced Fibre Distortions (SYDs) and have got a wedge shaped geometry. Because a piece of Non-Crimp Fabrics NCF displays several stitch yarn penetration points, you’ll find so many SYDs which intersect one another. To find out the intersection points, we also built an intersection search algorithm. Nodes were defined at these points and 1D elements were made in between. These 1D elements show the flow channels through the NCF and were put together in a system of equations. In the beginning, the model forecasted an extremely anisotropic permeability that is certainly impractical. To strengthen this model, it was extended with details which take into account stitch yarn affected regions. External channels are made by the stitch yarns, running from one stitch yarn penetration location to another. The regions in the Stitch Yarn induced Fibre Distortions SYDs with the penetrating stitch yarns were also added. These regions were explained by a small assembly of 1D elements. We carried out parametric studies with flow simulation software to describe the properties of these elements . Ultimately, a network of elements which stand for the flow domain of the Non-Crimp Fabrics NCF was developed and the model was perfected to get solutions for both steady state and transient (fill simulation) situations.


1 Introduction
1.1 CFRPs and Production Methods
1.2 Motivation and Objective
1.3 Permeability
1.3.1 Theoretical Assumptions to Obtain Darcy’s Law
1.3.2 Practical Permeability Usage
1.4 Brief Overview of this Research Area
2 Geometry Modelling
2.1 Manufacturing and Resulting Structure of Non-Crimp Fabrics NCFs
2.2 Stitch Yarn induced fibre Distortions
2.2.1 Intersection Search
2.3 Model Extensions
2.3.1 External Channels
2.3.2 Stitch Yarn induced Fibre Distortions SYD Domain Obstacles
3 Flow Modelling
3.1 Channel Flow
3.2 Non-Crimp Fabrics NCF Meso Level based Flow Models
3.2.1 Multidimensional Flow Domain
3.2.2 One-Dimensional Flow Domain
3.3 Stitch Yarn induced fibre Distortions
3.4 Model Extensions
3.4.1 External Channels
3.4.2 SYD Domain Obstacles
4 Network Flow Model
4.1 Numerical Program
4.2 Steady State Solution
4.2.1 Sensitivity Analyses
4.3 Transient Solution
4.3.1 Filling Scheme
4.3.2 Results Contents
5 Experiments
5.1 Experimental Set-Up
5.2 Permeability Determination
5.2.1 Quasi-Steady State Based
5.2.2 Flow Front Position Based
5.2.3 Flow Front Speed Based
5.3 Results
5.3.1 Data Analyses
5.3.2 Visual Observations
5.4 Evaluation
6 Discussion
6.1 Steady State Model Results
6.1.1 Variable SYD Lengths
6.1.2 Variable Stitch Yarn induced Fibre Distortions SYD Heights and SYD Widths
6.1.3 Isotropy of the Permeability (Model vs. Experiment)
6.1.4 Influence of Added Details and SYD Dimensions
6.1.5 Permeability Range Comparisons
6.2 Recapitulation and Recommendations
6.2.1 Steady State Model
6.2.2 Fill Simulation
6.2.3 Conclusive Model Verification
7 Conclusions
7.1 Steady State Model Configuration
7.2 Experiments vs. Steady State Model
7.3 Transient Model Configuration
A Derivation of Stitch Yarn induced Fibre Distortions SYD intersection points
B.1 ANSYS CFX-5 shape functions
C Domain Obstacles
D Solution Accuracy for External Channels
D.1 Extruded Layers
D.2 Mesh Size
D.3 Reynolds Number Dependence
D.4 Results External Channels
E Solution Accuracy for SYD Domain Obstacles
E.1 Reynolds Number Dependence
E.2 Mesh Size……….

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Source: University of Twente

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