Towards Tailored Composite Bonded Repairs (BONDPAIR)

目前，先进复合材料在飞机结构（主要和次要部件）中得到了很大程度的应用（例如，波音787、空客A350和庞巴迪c系列中占重量的50%）。对于这些具有大型复合材料部件的新一代飞机结构，现有的修复技术必须得到显著改进，以制造坚固、可靠和可认证的修复，以恢复受损（例如冲击载荷）的主要结构部件。重要的是要注意到飞机的主要结构部件对飞机的结构完整性和安全性至关重要。主要部件负载高，相对较厚（范围从~ 3mm到~ 25mm），其中几层具有不同的纤维取向，因此需要先进的修复设计和制造技术来恢复原始结构/操作条件。在这方面，目前的修复设计和制造方法需要显著改进，以修复初级复合材料飞机结构。由于紧固件引起的应力集中，机械紧固的复合材料修复对于聚合物复合材料结构来说并不理想，而结合围巾修复可以提供高连接效率和空气动力学表面光洁度，为改进复合材料修复方法提供了机会，因此在飞机维修中具有更大的潜力。物质损害的程度往往是不确定的，取决于损害的来源/性质。围巾修复需要从母部件中去除的材料量不仅取决于材料损坏的量，还取决于所设计的补丁的几何参数（例如补丁形状，围巾角度）。为了达到设计的贴片几何形状，需要在受损区域周围加工大量未损坏的材料。此外，去除的未损坏材料的数量可能对设计用于承受高应力的部件产生不利影响。为了最大限度地减少从组件中移除未损坏的材料，围巾修复的设计应该针对给定的修复条件进行定制。另一方面，需要开发新的制造技术来实现复杂的贴片几何形状（例如，母体层压板的精确加工，配套贴片的固化）。在此背景下，提出的研究重点是使用非传统的围巾补丁几何形状对初级复合材料结构进行定制复合材料粘合修复。该项目旨在(a)开发一种新型的基于灌注的修复方法，使用易于储存的材料（碳纤维织物、热塑性面纱）制造围巾修复，而不使用预浸料和薄膜粘合剂；(b)通过结合非传统的贴片几何形状来增强贴片界面应力分布，从而最大限度地减少母部件未损坏材料的数量。(c)描述了定制围巾修复的失效行为，并与常规围巾修复进行了比较。该研究项目的目标是开发科学途径，使未来的维修技术成为可能，特别是为飞机结构中的主要复合材料部件量身定制。

Advanced composites are currently being used in aircraft structures (primary and secondary components) to a significant extent (e.g. 50% by weight in Boeing 787, Airbus A350 and Bombardier C-Series). For these new generation of aircraft structures with large composite components, the existing repair technology must be significantly improved to fabricate robust, reliable and certifiable repairs for restoring damaged (e.g. impact loads) primary structural components. It is important to note that primary aircraft structural components are critical to aircraft structural integrity and safety. The primary components are highly loaded and relatively thick (ranging from ~3 mm to ~25 mm) with several laminae having different fibre orientations, and thus require advanced repair design and fabrication techniques to restore the original structural/operational conditions. In this regard, current repair design and fabrication approaches need to be significantly improved for repairing primary composite aircraft structures. As mechanically fastened composite repairs are not ideal for polymer composite structures because of the stress concentrations induced by fasteners, bonded scarf repairs, which can provide high joint efficiency and aerodynamic surface finish, offer opportunity to improve composite repair methodology and thus have greater potential for aircraft repairs. The extent of material damage is often uncertain and depends on the source/nature of damage. The amount of material that needs to be removed from the parent component for a scarf repair not only depends on the amount of material damaged but also the geometrical parameters (e.g. patch shape, scarf angle) of the patch designed. A significant amount of undamaged material around the damaged region needs to be machined in order to achieve the designed patch geometry. In addition, the amount of undamaged material removed can have an adverse effect on a component that is designed to take high stresses. To minimize the removal of undamaged material from the component, the design of scarf repairs should be tailored for a given repair condition. On the other hand, novel fabrication techniques need to be developed to achieve complex patch geometries (e.g. accurate machining of parent laminate, curing of a mating patch).In this context, the proposed research is focused towards tailored composite bonded repairs to primary composite structures using non-conventional scarf patch geometries. The project aims to (a) develop a novel infusion-based repair methodology to fabricate scarf repairs using easy-to-store materials (carbon fibre fabric, thermoplastic veils) without pre-preg and film adhesives, (b) minimize the amount of undamaged material from the parent component by incorporating non-conventional patch geometries for enhancing parent-patch interface stress distribution, and (c) characterising failure behaviour of tailored scarf repairs and comparing with conventional scarf repairs. The ambition of this research project is to develop scientific pathways that will enable future repair technologies, especially tailored for primary composite components in aircraft structures.