Safety evaluation of mooring chains under tension and bending moment considering ratchetting behaviour

Paper in proceeding, 2026

This study aims to investigate the plastic behaviour of a mooring chain under extreme tensile loading conditions using nonlinear finite element analysis. The plastic response of mooring chains is crucial for maintaining structural integrity under repeated environmental loads. The analyses were performed under cyclic tension and cyclic bending to evaluate the evolution and stability of the plastic behaviour of an R3-grade mooring chain with a nominal diameter of 100 mm. The plastic material properties adopted in the analysis were defined using the Ramberg–Osgood relationship. For cyclic tension, the load amplitude was gradually reduced based on the break load, and the results indicated that stable plastic behaviour was achieved at approximately 80% of the break load, while a conservative limit of 70% or lower is recommended for safe operation. Under cyclic in-plane bending (IPB) and out-of-plane bending (OPB), the accumulated plastic strain increased with the tension angle, and the OPB produced slightly higher deformation than the IPB. At a tension angle of 3°, ratchetting behaviour was observed, indicating that small angular displacements under high tensile forces can still induce progressive plastic deformation. The findings highlight the importance of considering ratchetting and shakedown phenomena in the structural design and safety assessment of mooring chains subjected to extreme cyclic loads.