Validation of a multiaxial finite element fatigue model for mooring chains under constant amplitude loading

Mooring chains are critical components in floating offshore energy systems, where fatigue failure may compromise structural integrity and operational reliability. Conventional fatigue assessment is generally based on standard S-N or T-N curves, which do not explicitly capture the local multiaxial stress–strain conditions governing crack initiation. This work develops and validates a finite element (FE) multiaxial fatigue methodology for chain links under constant-amplitude tension-tension loading. Elasto-plastic FE simulations of three-link chain assemblies are combined with the Smith-Watson-Topper (SWT), Walker, Fatemi-Socie and Dang Van criteria to evaluate fatigue indicator parameter distributions and predicted fatigue lives. The numerical predictions are validated against fatigue tests performed on commercial DIN 764 studless chains and supported by fracture surface observations. The results show that fatigue failure is governed by competing critical regions at the outer crown and kt point, while contact-zone damage is mainly associated with local fretting. The SWT and Walker criteria reproduce the experimentally observed mode I failure regions, while Walker provides the best fatigue life predictions, with all but one estimate within a factor of two of the experimental results. The improved performance is attributed to its calibrated mean-stress sensitivity. The Walker criterion provides the most suitable balance between physical consistency and quantitative prediction capability for the tested chain links.