Development of a Wear Coupon Test Machine to Reproduce the Severe-Mild Wear Transition for Mooring Chains of Floating Offshore Wind Turbines

Abstract In pursuit of a carbon-neutral society by the year 2050, floating offshore wind turbines (FOWTs) garner heightened expectations. Mooring chains are commonly employed for the station-keeping of FOWTs, and long-term use can cause failure attributable to diameter reduction due to wear and corrosion. Among these, interlink wear caused by floating body motion can be estimated by dynamic analysis. However, it is important to accurately determine the wear characteristics to estimate the wear allowance properly. Gotoh et al. [11] conducted the wear test reproducing inservice behavior and confirmed the occurrence of a severe-mild wear transition which represents the change from initial wear to steady-state wear. However, such a phenomenon was not observed in the coupon test previously performed by the authors under fully submerged conditions. This could be a difference in sliding speed and contact stress. In this study, a wear test machine capable of applying high load was developed using heat-treated surfaces under fully submerged conditions to investigate those characteristics. In the wear test, test specimens with Grade R3 and 60 mm diameter are pressed against each other by hydraulic cylinder with a maximum load of 200 kN, and these were slid by controlling the displacement of the wear test jig installed in the fatigue testing machine. The wear behavior was investigated under several sliding speed and loading conditions. As a result, the severe-mild wear transition was observed under high stress in this coupon test, and it was found that slower speeds tend to delay its onset.