Composite overmoulding for complex, multifunctional loaded structures

热塑性半晶复合材料由于其具有在高温下重塑和融合的能力等具有吸引力的特性而重新引起了人们的兴趣和需求。这使得它们成为新结构部件、增材制造材料、粘合剂和涂料等新兴应用的理想候选者，以及需要可重复使用、经济和功能性产品的应用。热塑性塑料热焊接过程中热熔界面的质量非常重要，因为再生界面对复合材料的整体性能起着至关重要的作用，并且在航空航天应用中对复合材料的增韧起着重要作用。两种热塑性塑料融合的过程称为界面愈合，描述了发生的多尺度物理过程。界面愈合过程控制着后续的界面性能，影响着整体力学性能。目前，没有设计工具或确定的方法可以预测这些热塑性界面的界面强度，特别是在复合材料复模的背景下，这是一种用于创建3D结构部件的制造工艺。这是因为目前大多数研究界面愈合的模型都是基于最初为非晶聚合物开发的理论，然后适用于半晶聚合物。此外，这些模型没有考虑结晶，这是半结晶聚合物加工中需要考虑的最重要的相变。结晶分布将影响界面性能，进而影响体性能。此外，在形成热塑性界面时采用的制造工艺也会影响结晶分布，从而为该过程的建模增加了另一个层次的复杂性。这项博士研究的目标是：-开发一种工具来模拟热塑性复合材料的结晶厚度。-对热焊接过程中的冷却循环进行优化试验，以提高界面的结晶度-制造具有潜在梯度结晶度结构的热塑性复合材料样品。该模型工具将能够为热塑性复合材料制造中的冷却循环优化提供信息。它还将为多尺度界面愈合模型的开发提供更多关于非等温结晶建模的信息，并允许制造具有更高界面结合强度的3d形状热塑性复合材料的新方法。

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.