Cyclic behavior and strain energy-based fatigue damage analysis of mooring chains high strength steel. (March 2020)

• Record Type: Journal Article
• Authors: Zarandi, Ershad P.; Skallerud, Bjørn H.
• Is Part Of: Marine structures. Volume 70(2020)
• Publication Date: 2020-03
• Subjects: Strain energy density -- Fatigue life prediction -- Cyclic plasticity -- Hardening/softening -- Finite element -- Offshore mooring chain; Naval architecture -- Periodicals; Offshore structures -- Periodicals; Architecture navale -- Périodiques; Structures offshore -- Périodiques; Naval architecture; Offshore structures; Periodicals; 620.4162
• DOI: 10.1016/j.marstruc.2019.102703
• Languages: English
• ISSNs: 0951-8339

Abstract

Abstract: This study investigates the low-cycle fatigue behavior of mooring chains high-strength steel grade R4 under different strain amplitudes and strain ratios at room temperature. A fatigue test program has been carried out on small low cycle fatigue specimens cut from large mooring chains. The experimental results characterize the cyclic stress-strain relationship, the mean stress relaxation behavior, and the cyclic plasticity parameters of the material. Strain energy density is correlated with fatigue life through a simple power-law expression and very well represented by Basquin-Coffin-Mansion relationship. Further, a non-linear elastic-plastic material model is calibrated to the experimental stress-strain curves and used for the estimation of energy dissipation in the specimens under applied cyclic loads. The predicted fatigue life using the calibrated material parameters demonstrates a close agreement with the experimental fatigue life. Numerical simulations are carried out to analyze local plastic straining and assess crack initiation at the pit site of corroded mooring chains considering the multiaxial stress state. An energy-based approach is employed to estimate the number of cycles needed for a crack to initiate from an existing corrosion pit. Highlights: The experimental data has revealed that the material experiences rapid cyclic softening for all strain ranges studied. The material's fatigue and hardening parameters have been characterized and calibrated to the experimental data. The fatigue life was estimated using SED approach. A decent agreement was observed between the experimental and predicted life. The predicted initiation life has been estimated to be 20–40% of the total life of corroded chain links tested in the lab. The effect of the mean load on the crack initiation life of corroded chains has been captured.