Remaining life assessment method of fatigue crack propagation in a double hull ship structure

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The fitness for serviceability of structural members of ships, in which fatigue cracks could be found during in-service inspection, is investigated in order to prevent instantaneous failures of ships as well as the loss of serviceability such as oil and/or water tightness of critical compartments. The characteristics of fatigue crack propagation and the remaining life assessment of double hull ship structures are discussed.A finite element comparative study of ship structural detail has been carried out in order to examine the possible variations of calculated local stress by practitioners. It is found that the results of shell element models have high correlation with each other, but give significantly lower local stress than experimental and solid element results. With regard to the analysis of 3-D cracks, a new combined numerical and analytical weight function method is proposed for the determination of stress intensity factors in ship structural details, which is proved to be a ver … More y efficient method for fatigue crack analysis. Discussions are also made for an advanced numerical simulation method for the remaining life assessment, in which the effects of welding residual stresses, structural redundancy, and curved crack propagation are precisely taken into account. The simulated crack paths and the fatigue crack propagation lives are in fairly good agreement with the experimental results.The fatigue remaining life assessment is demonstrated for cracks detected in the critical parts of the inner bottom plate of a double bottom structure, where the remaining life is calculated based on the fracture mechanics approach. The paving method and the domain composition method are implemented for the efficient and robust finite element mesh generation which is essential for fatigue strength analysis and fatigue crack propagation analyis. Also, an advanced computational method has been developed for the prediction of curved crack growth. A concept of the information system for damages of ship structures is proposed for the improved safety and maintenance of ships in service. Less