Consideration of Creep and Relaxation on the Fatigue Life of Copper Conductors in Dynamic Cables

Abstract Dynamic cables play a critical role in floating offshore energy infrastructure such as needed for floating wind and electrification of oil and gas assets. Steel alloys used for cables, umbilicals and flexibles have seen a wide range of work on their mechanical properties combined with a substantial track-record. The same cannot be said for copper conductors for which only a few studies have been undertaken accounting for a limited parameter range. One parameter that should be studied further is the effect of intermittent creep damage due to the interplay between the conductors' mean stress and loading history under displacement-controlled deformation. New and existing copper fatigue test data are used to establish a mean-stress sensitive fatigue damage model. This is used to estimate the added damage from the relaxation phase, and allows us to compare displacement- and load-controlled tests and compile the data into a unified model. The effect of this model is then assessed in light of potential loading histories.