An engineering method to predict fatigue crack propagation life for marine structures

Accurate prediction of fatigue life is important for the safety of marine structures. Comparing with traditional methods based on Cumulative Fatigue Damage (CFD) theory, life prediction based on Fatigue Crack Propagation (FCP) can take the key factors, like load sequence and initial defects, into consideration. This makes the major classification societies strongly promote the application of FCP theory in ocean engineering. This paper investigated the engineering method of fatigue life prediction based on FCP from three aspects, namely crack propagation law, calculation of Stress Intensity Factor (SIF) and generation of fatigue load spectrum. The aim was to find an accurate, rational and relatively simple method. By using the unique curve model, the technology of sub-model to calculate SIF and the method to generate fatigue load spectrum based on spectral analysis, the crack propagation life of a typical fatigue hot spot of a semi-submersible platform was predicted and then the effect of initial crack size was discussed. The results showed the discussed hot spot met the requirement of design life. And initial crack size of the surface crack affected the fatigue life a lot. The method proposed in this paper may provide a reference for accurate prediction of fatigue life of marine structures. © 2016, Editorial Board of Journal of Ship Mechanics. All right reserved.