This paper outlines an experimental investigation into the durability of large-scale adhesively bonded joints immersed in a 3.5 wt% NaCl solution for 10 weeks at 50°C. Two aged and one unaged specimen were subjected to tensile testing up to failure, and three aged and one unaged specimen were loaded up to ~3.5 million fatigue cycles followed by a residual tensile test. The shear, longitudinal, and peel strain values in adhesive bulk (evaluated by the digital image correlation (DIC) technique) are significantly higher at the gripped sides due to the asymmetrical design of the steel brackets. The shear strength and stiffness of statically and fatigue tested specimens are found to be identical. The shear strength values are significantly higher than the requirements following from the design. All specimens failed by sudden delamination of the composite plate. Post-mortem analysis showed no corrosion travel at the interface of steel and adhesive.

The present-day interest in the use of composite-steel joints in primary marine applications requires an in-depth knowledge of the fatigue performance of thick adhesive joints. This paper reports on experimental tests, quasi-static and fatigue, performed on unaged and aged bi-material double strap joints with thick adhesive bondlines. The specimens are monitored by Digital Image Correlation and Infrared Thermography techniques to evaluate the types and extent of damage that occur in the joint during fatigue loading. The S-N curve of the aged joint is evaluated along with it's fatigue limit. It is found that the unaged specimens fail due to cohesive damage, hackles and disbond at the adhesive-adherend interface and the aged specimens failed due to delamination within the composite. The specimens that survived fatigue loading showed similar residual strength as specimens that were not fatigue loaded.