Underwater Large-Scale Experimental Fatigue Assessment of CFRP-Retrofitted Steel Panels

Some steel structures, such as hydraulic navigation and marine structures, operate in harsh wet and corrosive environments and can suffer significant deterioration. The deterioration manifests itself in the form of corrosion, fatigue cracking, or a combination of both. Although typically viewed as a nuisance, if left unrepaired, the deterioration can threaten the integrity of the structure. Repairing these cracks using conventional repair methods has proven to be not only time-consuming but also ineffective. Recent advances in the use of carbon fiber–reinforced polymers (CFRPs) to retrofit structures have demonstrated its viability as a solution for increasing fatigue life of metal structures. However, the applications have been primarily focused on the aerospace and bridge industries, and very few studies have been concerned with retrofitting metallic structures under wet and corrosive environments. Therefore, there is a clear need to evaluate the possibility of using CFRP to repair underwater metal structures. To this end, this paper devises a new experimental setup to allow for underwater testing of large-scale steel panels retrofitted with CFRP patches. The purpose of this experimental study is to provide a first-of-its-kind benchmark data by which the potential for using CFRP for underwater fatigue repair of metallic structures can be assessed. Five large-scale steel panels are tested, three of which are repaired with CFRP patches, under different environmental conditions. The study evaluates the effect of CFRP retrofit on crack growth rate. Because the application in this study pertains to water navigation structures used in rivers, the effect of fluvial sediments and salt are considered. The use of salt allows for accelerated corrosion in the specimens to represent the actual condition of deteriorated panels. Test results for dry and underwater specimens show an increase in fatigue life with the use of CFRP compared with bare specimens. The results also show an increase in debonding susceptibility of the CFRP when the CFRP/adhesive system is subjected to corrosion, turbulence, and sediment particles.