Mass reduction is one of the main drivers for aircraft design. A big potential for saving mass can be found in part joining. Currently, most parts are joined by mechanical fastening. However, mechanical fastening requires labor intensive work and results in a weight increase especially for composite parts that, due to the mass saving they allow, are increasingly used in the aerospace industry. Induction welding of thermoplastic composites shows great potential to limit this mass increase and it can vastly reduce the amount of work that is needed to join parts while improving the working conditions on the shop-floor. A characteristic of induction welding is that the heating rate goes down with increasing distance to the inductor. This often leads to fully melting the top plate across its thickness. This results in an imperfect weld as pressure is required for proper consolidation which leads to a damaged surface. Therefore, the challenge is to find a way to selectively heat the weld zone, without using a metallic susceptor that can lead to an unreliable joint. Accordingly, the aim of this thesis is to find how induction heating can be used to selectively heat the weld zone of multidirectional carbon fiber laminates with and without using a carbon fiber susceptor material. To this end, three sub-questions are answered. Can specific plies in multidirectional CFRP laminates be heated by manipulation of the magnetic field? Can a carbon fiber material be used as susceptor material in order to increase the temperature at the weld interface? Is it possible to weld parts with lightning strike protection? Using an infrared camera and fine wire thermocouples of type E to measure the temperature profile across the thickness of the test parts, a dependency of the heating rate on the orientation of the magnetic field was discovered for all parts that were tested. This dependency can indeed be used to selectively heat plies in a specific orientation within the laminate. Also, the possibility of using susceptors made of carbon fiber to increase the temperature at the weld zone was shown. To this end, susceptors were made of fabrics and of thin-ply material. Further research has to be done to improve these susceptor materials. An increase of the heating benefit they deliver could enable them to be used for more efficient welds in the future. Finally, by clamping lightning strike protection (LSP) onto the test parts, the temperature profile of parts with LSP was imitated. Striking was that the heat generated in the two CFRP parts went down when the LSP was added. No peak temperature was measured at the side of the LSP but this could probably be explained by the poor contact between the thermocouple in the test part and the LSP. It is recommended to further investigate this topic by consolidation of the LSP onto the test part.

In modern aircraft, structural lightweight composite components are increasingly used. To manufacture these components in a costeffective way, robust production systems for the manufacturing of complex fibre composite components are necessary. A rather novel but already established process for fibre material deposition is the Automated Fibre Placement (AFP) technology, which automatically places several narrow, parallel fibre tows on a mould. Typically, a component consists of several, often hundreds of stacked layers of these fibre material strips. However, when these narrow fibre tows are placed in position, layup defects can occur and reduce the mechanical properties of the component. Hence, in safety critical applications, such as aircraft manufacturing, a visual inspection of every single ply is mandatory. This inspection step is currently carried out by an expert via a visual examination, which requires up to 50 % of the total production time. An automation of this inspection process using suitable algorithms offers great potential for increasing process efficiency. However, with the growing complexity of these respective defect analysis algorithms, their performance potentially increases, but the comprehensibility of the machine decision and the behaviour of the algorithm become more challenging. This is problematic especially in safety critical applications. In addition, the data quality of recorded images is influenced by the very matte, low reflective Carbon Fibre Reinforced Plastic (CFRP) material which raises the uncertainty of an inspection.... @en

Composites are increasingly used in the aerospace industry due to their lightweight potential and flexible design options. The most widespread manufacturing process for large components made of fibre composites is still the open mould process. In this process, a composite component is placed on a mould and hermetically sealed with a vacuum bag consisting of vacuum film and other auxiliary materials. The function of this vacuum bag is to evacuate possible air inclusions and to transfer the pressure evenly to the component during curing in an autoclave. If the vacuum bag is not tight, the quality of the final product can be affected. Leakages in the vacuum bag lead to porosities and defects in the component and must therefore be avoided by all means. Even though conventional leakage detection techniques are generally able to detect leakages in vacuum bags, they are usually considered as inaccurate and very timeconsuming. Within a market study, performed in this work, it is found that the most promising method for efficient and automated leakage detection is a combination of volumetric flow rate measurement and infrared thermography. The tightness of the vacuum bag is checked with the help of the volumetric flow rate measurement and, in the event of a leak, the affected area can be narrowed down with the help of the flow data. Afterwards, the exact position of the leakage within this area is determined by means of infrared thermography and can thus be remedied. In order to be able to assess the effects of leakage on vacuum bags, theory, experiment and numeric are subsequently linked to be able to make a valid statement about the condition within the vacuum setup. It is shown that both the volume flow rates and the pressure gradient that occurs as well as the temperature and air velocity in the area of a leakage can be simulated. These effects in turn have an impact on the subsequent component quality. To investigate their influence, various autoclave tests with different types of leakage are carried out and evaluated. It is shown that leakages where there is a direct connection between the laminate and the environment are significantly more critical, regarding porosities, than those where the laminate is still protected from inflowing air by an intact release film. The use of machine learning in leak detection subsequently shows further potential for improving localisation, especially in the case of multiple leaks in the component. The costs of leakages in the composite component manufacturing process are typically hidden in the overall production costs. To address this, this research also examines the financial impact of leakages and the estimated financial benefits of implementing an advanced leakage detection process. Overall, this research shows that the improved leakage detection, analysis of the impact of leakage in the vacuum bag and on the component, and implementation of machine learning will increase the efficiency, effectiveness, and sustainability of the open mould process. @en