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

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.