Fatigue Strength Assessment of Large-scale Ship Structures

In the traditional ship structure fatigue strength assessment only high cycle fatigue is taken into account,while the low cycle fatigue has usually been neglected.However,with the development of large-scaled ship structure and the damage of offshore structure,much attention has been focused on the low cycle fatigue.Urm et al.has investigated the low cycle fatigue of the tanker structure generated by the cargo loading and unloading and developed a simplified procedure.Since many problems have not been solved,it is necessary to further the study on the reason and assessment approach of the low cycle fatigue of the ship structure.In this paper,the reason and assessment approach have been presented and the quantitative results have been obtained.Based on the mechanism of the low cycle fatigue,the analysis of the low cycle life region extrapolated by the existing S-N curve is conducted and compared with the experiment.In addition,the fatigue damage interaction between the small amplitude fatigue load caused by the wave loads and large one owing to the full load and ballast has been analyzed,and a nonlinear cumulative damage model is developed.