Effect of marine atmosphere on the fatigue behavior of CFRP strengthened steel plates

Fatigue still represents one of the most detrimental causes of steel structure failure. Carbon fiber-reinforced polymer (CFRP) composites offer a good opportunity in structural repair because of their high strength-to-weight ratio and the possibility to obtain the material in different forms, which can fit all desirable geometries. Commonly, steel structures experience either service load and environmental exposure simultaneously, and however, the effect of this combination is still not analyzed enough nowadays, especially in fatigue terms. This paper highlights an experimental analysis of the fatigue performance of steel plates repaired with CFRP laminates subjected to the marine environment. Five degrees of initial damage to the steel plates were considered. The bond consisted of one layer of CFRP laminate adhesively bonded on both sides of the plate with two different patches, i.e., fully covered and partially covered. The specimens were exposed to a simulated marine atmosphere for up to one and six months. In order to reproduce service load stress, the plates were subjected to a static tensile load during exposure. After submergence, the fatigue life was tested at room temperature and the crack propagation was monitored throughout the beach marking technique. The effect of environmental exposure on the epoxy was also carefully investigated. The improvements provided by CFRP bonded to steel were successfully maintained after exposure to harsh environmental conditions although decrements of fatigue life were accounted after six months of exposure. The decrements of the fatigue life due to the environmental effect ranged from 3% to 30% compared to the unexposed specimens. Marine atmosphere mostly affected the integrity of the interfaces, since adhesion failures occurred progressively from one to six months of exposure. The work provides useful recommendations for practical purpose and it suggests topics which require further investigation.