Testing of new adhesive and CFRP laminate for steel-CFRP joints under sustained loading and temperature cycles

The influence of combined mechanical and environmental loads on the behaviour of CFRP strengthened steel structures is crucial for their safe use and effective design, and requires further fundamental investigations. Past studies have shown that 'catastrophic' failure of steel-CFRP joints can occur under just 15% of the ultimate load during long term exposure to wet thermo-mechanical loading. In this paper, the results of an experimental investigation into the effects of thermo-mechanical loading in both wet and dry conditions on steel-CFRP single-lap joints are presented. Two types of CFRP and a new adhesive that has a glass transition temperature (Tg) of 82 °C are used in the study. The results revealed no failure in the joint during exposure to thermal cycling between 10 °C and 50 °C, with and without an applied sustained load, in both wet and dry conditions and with little degradation in the residual bond strength. It was recommended that the Tg of the adhesive should be at least 30 °C greater than the highest service temperature in order to avoid failure under thermo-mechanical loading. It was also recommended to seal the adhesive joint with water-proof sealant in the CFRP repair system to prevent the ingress of moisture.