Airflow Based Quality Measurements of Semi-Finished Textiles: Developments and Investigations towards a Novel Non-destructive Injectability Measurement for Fibre Preforms

Abstract

Composites are a superior material and can outperform any classical engineering material (e.g. steel, aluminium). Excellent mechanical properties in combination with low specific density are the perfect ingredient for new exciting and ground-breaking products. Undoubtedly, this benefit comes with a major drawback. With a shifting perception towards environmentally friendly and sustainable production methods, composites present a challenge. The industry-wide scrap rate of almost 30 % significantly affects the environmental and economical balance of this material class. Providing novel quality control tools to avoid scrap can transform costs into profits and help reduce the environmental impact. In this thesis, methods and technologies to efficiently reduce scrap rates with non-destructive testing were developed, including material and feature characterisation for multi-ply semi-finished textiles (e.g. stacks, preforms). This thesis conjoins a strong industrial background with the specific research area of fluid flow in porous media. A set of experiments was carried out to investigate the potential of air-flow based quality measurements for feature and defect detection. The resistance due to fluid flow of semi-finished textiles was characterised in a fast, clean and non-destructive manner. The presented research focuses on the flow mechanics during the non-destructive quality assessment of semi-finish textiles. Moreover, this assessment provides information about different flow effects appearing at certain flow regimes. Five different flow scenarios for fluid flow through porous media were evaluated (Darcian flow, Compressible flow, Klinkenberg flow and incompressible and compressible Forchheimer flow) by comparing analytical solutions with the experimental data. The focus was on theoretical and experimental comparison of permeabilities and flow velocities with a refined view on the corresponding pressure distribution. A pressure mapping technique was developed and utilised to examine the pressure distribution during the air injection. These experimental results were then compared to analytical solutions providing further information on the flow characteristics. This correlation is essential for the assessment of various effects and to study comprehensively the flow mechanics induced by the non-destructive quality assessment of semi-finished textiles. Influences arise from the compressibility of the test fluid as well as from the injection pressure and velocity and these should all be quantified. An industrial prototype was developed detecting different material features by interpreting injectability and compressibility of multi-ply semi-finished textiles. The developed device provides fast, robust and easy-to-interpret measurements. In contrast to already acknowledged and more complex quality monitoring techniques (e.g. eddy current, permeability determination) the proposed method is ready for “Smart Production” and “Industry 4.0”. The results generated by the injectability measurements can easily be transformed into quantitative values enabling real-time process control. Process limits can be defined to assist preventive maintenance, detect wear or address other issues causing production problems. Cause-and-effect relations between the process and semi-finished products can be assessed, and the economic balance of production processes and use of resources can be enhanced. The presented solutions in general characterise the resistance of semi-finished textiles to fluid flow as a quantitative indicator of their processability and provide a practical and efficient means of assessing the quality of semi-finished textiles compared to already acknowledged technologies.Composites are a superior material and can outperform any classical engineering material (e.g. steel, aluminium). Excellent mechanical properties in combination with low specific density are the perfect ingredient for new exciting and ground-breaking products. Undoubtedly, this benefit comes with a major drawback. With a shifting perception towards environmentally friendly and sustainable production methods, composites present a challenge. The industry-wide scrap rate of almost 30 % significantly affects the environmental and economical balance of this material class. Providing novel quality control tools to avoid scrap can transform costs into profits and help reduce the environmental impact. In this thesis, methods and technologies to efficiently reduce scrap rates with non-destructive testing were developed, including material and feature characterisation for multi-ply semi-finished textiles (e.g. stacks, preforms). This thesis conjoins a strong industrial background with the specific research area of fluid flow in porous media. A set of experiments was carried out to investigate the potential of air-flow based quality measurements for feature and defect detection. The resistance due to fluid flow of semi-finished textiles was characterised in a fast, clean and non-destructive manner. The presented research focuses on the flow mechanics during the non-destructive quality assessment of semi-finish textiles. Moreover, this assessment provides information about different flow effects appearing at certain flow regimes. Five different flow scenarios for fluid flow through porous media were evaluated (Darcian flow, Compressible flow, Klinkenberg flow and incompressible and compressible Forchheimer flow) by comparing analytical solutions with the experimental data. The focus was on theoretical and experimental comparison of permeabilities and flow velocities with a refined view on the corresponding pressure distribution. A pressure mapping technique was developed and utilised to examine the pressure distribution during the air injection. These experimental results were then compared to analytical solutions providing further information on the flow characteristics. This correlation is essential for the assessment of various effects and to study comprehensively the flow mechanics induced by the non-destructive quality assessment of semi-finished textiles. Influences arise from the compressibility of the test fluid as well as from the injection pressure and velocity and these should all be quantified. An industrial prototype was developed detecting different material features by interpreting injectability and compressibility of multi-ply semi-finished textiles. The developed device provides fast, robust and easy-to-interpret measurements. In contrast to already acknowledged and more complex quality monitoring techniques (e.g. eddy current, permeability determination) the proposed method is ready for “Smart Production” and “Industry 4.0”. The results generated by the injectability measurements can easily be transformed into quantitative values enabling real-time process control. Process limits can be defined to assist preventive maintenance, detect wear or address other issues causing production problems. Cause-and-effect relations between the process and semi-finished products can be assessed, and the economic balance of production processes and use of resources can be enhanced. The presented solutions in general characterise the resistance of semi-finished textiles to fluid flow as a quantitative indicator of their processability and provide a practical and efficient means of assessing the quality of semi-finished textiles compared to already acknowledged technologies.