Failure process and optimal design of hybrid adhesive joints - a microscale experimental and numerical approach

随着工程新材料的不断发展，混合结构通过采用新材料代替传统材料来获得理想的性能，得到了广泛的应用。在汽车、航空航天和国防工业中尤其如此，因为这是实现增强性能、提高燃油效率和减少温室气体排放的主要方法。这种技术正在德国和美国等其他以高价值制造业为基础的经济体迅速得到利用。在混合结构制造中，粘接技术因其具有成本效益高、结构集成度高、载荷分布均匀、损伤容忍度高的优点而备受关注。然而，粘接技术在混合结构中的应用仍有一定的局限性。“混合接头”的概念涉及两种或多种不同成分的组合，具有不同的材料性能。到目前为止，还没有一个完善的理论可以描述混合接头的组分组合、几何形态（界面和胶层的微观结构、胶粘剂的厚度和重叠等）与混合接头整体性能之间的关系。此外，混合胶接头的优化是另一个挑战，因为混合胶接头的可能有效因素数量明显高于常规接头，并且这些因素是相互作用的。在实际应用中，对混合动力节点没有有效的优化方法。这些限制导致了“过度设计”混合连接结构的趋势。因此，该项目将专注于混合胶粘剂接头失效机制的基础研究，并制定优化策略，这将与学术界和工业界的观点保持一致。为了实现这些目标，项目有四个主要的工作包（wp）。在WP1中，将使用先进的测试设备分析接头的破坏机制，并考虑微观结构的影响。然后，在WP2中，将开发DEM模型来描述关节的力学特性并生成优化所需的数据点。基于WPs 1和WPs 2的结果，WP3将使用DoE和遗传规划技术开发优化算法，根据设计要求生成混合胶合接头的最优设计。最后，案例研究将基于实际应用进行验证。该项目的成果将大大克服该领域目前研究的局限性，并允许在高价值制造中开发高性能混合结构的阶梯式变化。

With development of new engineering materials, hybrid structures are now widely used to achieve desired performances by applying new materials instead of conventional ones. This is especially so in the automotive, aerospace and defence industries, since it is a major method to achieve enhanced performance, better fuel efficiency and to minimise greenhouse gas emissions. This technique is being rapidly exploited in other high-value manufacturing-based economies such as Germany and the US. To fabricate hybrid structures, adhesive joining technique attracts more attentions due to their advantage of enabling cost-effective, highly integrated structures with a uniform load distribution and improved damage tolerance. However, there are still some limitations to the use of adhesive joining in hybrid structures. The concept of "hybrid joint" involves a combination of two or more different constituents, with different material properties. To date, there is no well-established theory, which can describe the relationships among the combination of constituents, geometric configuration (microstructures of interfaces and adhesive layer, thickness and overlap of adhesives, etc.) and the overall performance of a hybrid joint. Furthermore, optimization of hybrid adhesive joints is another challenge, since the number of possible effective factors for hybrid adhesive joints is significantly higher than conventional joints and the factors are interactional. In practice, there is no effective optimization method for hybrid joints. Those limitations have resulted in the tendency to "overdesign" hybrid-joining structures. Therefore, the project will focus on a fundamental study of failure mechanisms of a hybrid adhesive joint, and the development of an optimization strategy, which aligns with perspectives from both academia and industry. To achieve the objectives, the project has four main work packages (WPs). In WP1, the failure mechanism of the joint will be analysed using advanced testing facilities, with consideration of the effects of microstructure. Then, in WP2, a DEM model will be developed to describe the mechanical properties of the joint and generate essential date points for optimization. Based on the results of WPs 1 and 2, an optimization algorithm will be developed in WP3 using DoE and Genetic Programming techniques for generating optimal design for hybrid adhesive joints according to design requirements. Finally, case studies will be carried out based on real-world applications for validation. It is intended that the outcomes of the project will substantially overcome the current limitations of the researches in this field and allow a step change in development of high-performance hybrid structures in high value manufacturing.