Durability of hybrid bolted-bonded joints under environmental aging on Helgoland

Hybrid bolted-bonded joints have emerged as a promising joining technology, combining the advantages of mechanical fastening and adhesive bonding to achieve enhanced strength, stiffness, and durability. This study examines the performance and environmental resilience of hybrid joints utilising two distinct adhesive systems: a two-component polyurethane (SF479) and an epoxy (SW7240). To ensure practical relevance, the selected steel substrate (S355MC) and fastening components (M12-10.9 bolts) reflect real-world applications of hybrid bolted-bonded joints in structural steel. A comprehensive series of tests was conducted through exposure to a maritime climate on the North Sea Island of Helgoland. This was done to simulate real-world environmental challenges over seasonal and year-long periods. The findings demonstrate that both adhesives demonstrate consistent load-bearing capabilities, with the epoxy adhesive displaying superior strength. Neither temperature fluctuations nor moisture ingress over the course of a year had a significant impact on the joints’ performance. The application of preloads up to 80% of the static load-bearing capacity did not result in any adverse effects on the structural integrity. Fracture analysis confirmed the occurrence of cohesive failure modes with minimal degradation, while moisture penetration simulations indicated that such conditions have a limited impact on adhesive integrity. These findings demonstrate the short-term robustness of hybrid bolted-bonded joints in challenging environmental conditions and highlight their potential for long-term structural applications. However, further research is required to fully understand and optimize this innovative joining technology, particularly in terms of its long-term durability.