An experimental investigation on nonlinear behaviors of synthetic fiber ropes for deepwater moorings under cyclic loading

•Nonlinear behaviors of synthetic fiber ropes including polyester, aramid and HMPE under cyclic loading are experimentally investigated.•The similarity criterion for dynamic stiffness of fiber ropes is derived and verified by experiments.•An empirical expression that can evaluate the evolution of dynamic stiffness under long-term cyclic loading is proposed.

The nonlinear mechanical behaviors of synthetic fiber ropes including polyester, aramid and HMPE under cyclic loading are of vital importance to the dynamic response and fatigue life of taut-wire mooring systems. In the present work, important topics including how the stiffness develops and how the main factors influence the evolution of dynamic stiffness as well as the nonlinear tension•elongation relationship are systematically investigated utilizing a specially designed experimental system. The similarity criterion for the dynamic stiffness of fiber ropes is derived from the dimensional analysis and verified by experiments. The empirical expressions of dynamic stiffness, which are currently used, are examined by the measured data. It is observed that the mean load is a main factor that significantly affects the dynamic stiffness; not only the effect of strain amplitude on the stiffness can not be ignored, but also the influence of loading cycles is of vital importance to the dynamic stiffness. Based on the measured data, an empirical expression that takes into account both the mean load, strain amplitude and number of loading cycles is proposed, which is the only one that can evaluate the evolution of dynamic stiffness under long-term cyclic loading.