Composite overmoulding for complex, multifunctional loaded structures

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Thermoplastic semi-crystalline composites have experienced a resurgence in interest and demand due to their attractive properties such as their ability to reshape and fuse at elevated temperatures. This makes them ideal candidates for emerging applications in new structural components, additive manufacturing materials, adhesives, and coatings as well as applications that require reusable, economical, and functional products. The quality of the heat-fused interface in the thermal welding process for thermoplastics is important as the regenerated interface plays a critical role in the bulk performance of the composite as well as plays a part in toughening the composite for aerospace applications. The process where the two thermoplastics are fused, known as interface healing, describes the multi-scale physical process that occurs. The interface healing process controls the subsequent interfacial properties, affecting the bulk mechanical properties. Currently, no design tool nor definitive method is available to predict these thermoplastic interfaces' interface strength, especially in the context of composite over-moulding, a manufacturing process used to create 3D structural components. This is because most current models looking at interface healing are based on theories initially developed for amorphous polymers and then adapted for semi-crystalline polymers. In addition, these models do not account for crystallisation which is the most important phase transition that needs to be considered in semi-crystalline polymer processing. The crystallisation distribution will affect the interfacial properties and in turn, affect the bulk properties. Additionally, the manufacturing process employed when forming the thermoplastic interface will also affect the crystallisation distribution adding another level of complexity to modelling this process. This PhD study will aim to: - Develop a tool to model the crystallisation through-thickness in thermoplastic composites. - Perform optimisation trials on the cooling cycle in the thermal welding process to improve the crystallinity at the interface - Manufacture a sample thermoplastic composite with a potential gradient crystallinity structure This model tool would be able to provide information for the optimisation of the cooling cycle in the manufacturing of thermoplastic composites. It will also provide more information on non-isothermal crystallisation modelling for the development of multi-scale interface healing models as well as allow for novel methods of manufacturing 3D-shaped thermoplastic composites with higher interfacial bond strengths.