Durability of CFRP/steel joints under cyclic wet-dry and freeze-thaw conditions

Strengthening of steel structures with adhesively bonded carbon fibre reinforced polymer (CFRP) materials have become increasingly popular in the last decade. However, uncertainties regarding the durability and long-term performance of CFRP/steel joints is a major obstacle for their growing application. Previous research indicates the deleterious effects of moisture and thermal cycles on the mechanical performance of these joints. To the authors' knowledge, the combined effects of moisture and thermal cycles have been scarcely investigated. This paper presents the results of extensive experimental investigations at material- and joint-level subjected to various cyclic environmental scenarios. Special consideration is given to the role of moisture, i.e. distilled- or salt-water, when combined with freeze-thaw cycles. Moreover, the possibility of providing a predictive modelling platform for residual strength prediction of environmentally aged joints using sequentially coupled moisture diffusion-fracture analysis is explored. The results show 11% and 47% strength reductions for the CFRP/steel joints after a complete wet-dry cycle in distilled- and salt-water, respectively, which are significantly larger than those observed after only the wet exposure. In addition, 125 and 250 freeze-thaw cycles were found to have no unfavourable effects on the strength of dry or preconditioned joints.